Sword of Plot Advancement



"For the king, for the land, for the mountains For the green valleys where dragons fly ''For the glory, the power to win the Black Lord I will search for the Emerald Sword!"

- Rhapsody of Fire, "Emerald Sword"

The Sword Of Plot Advancement is the offensive or defensive item that the central plot of the game revolves around, and whose collection by the player signifies that they are now capable of advancing to the end of the game. It thus marks the end of the Second Act.

Alternatively, it may be gained at the beginning of the Second Act, if it is important to game mechanics, and marks the beginning of the adventure proper.

Most of the time, since said sword acts as an Amplifier Artifact, it is the only Achilles' Heel of the immortal or Nigh Invulnerable Big Bad.

It isn't strictly a MacGuffin (which is meaningless in and of itself), because after it is attained and the dramatic tension surrounding it dissipates, it is still useful within the game's combat mechanics.

It contrasts with the Infinity+1 Sword, which is optional to the plot and is collected long after the protagonist ceases to require it. It is, however, somewhat of a headscratcher when said Infinity+1 Sword (and even the Infinity-1 Sword) is stronger; see Penultimate Weapon.

A sub-trope of both Plot Coupon and Plot Coupon That Does Something. Sister Trope to Second-Hour Superpower and Villain-Beating Artifact. Contrast It Was a Gift. See also Supernatural Aid.

Film

 * In Thor, Mjölnir serves this purpose.

Literature

 * The Sommerswerd in the second Lone Wolf gamebook Fire on the Water, which is also an Infinity+1 Sword that can be used in subsequent books in the series.
 * In Un Lun Dun, the UnGun.
 * Walt Disney's First Pen in Kingdom Keepers
 * The Sword of Shannara has the sword mentioned in the title
 * Kosall in The Acts of Caine
 * The Sword of the Lady in the Emberverse.
 * Narsil/Anduril in The Lord of the Rings: When Aragorn acquires the reforged sword, he gains new powers, one of which allows him to command an Army of the Dead, and overall it symbolizes his progression towards the throne of Gondor.
 * The Sword of Truth has the titular sword, which is a magically-imbued and has no equal. Richard gets it in like, the third chapter. Of the first book. Of a series of eleven doorstops. In fact, it becomes so associated with him and he actually reflexively reaches for it even when he doesn't have it, and other characters associate it with him personally. He eventually doesn't need it to kick twelve kinds of ass, but still prefers it to regular swords.

Video Games

 * The Master Sword in several The Legend of Zelda games, starting with A Link to The Past.
 * Yet it's sometimes a different sword, such as the Phantom Sword in Phantom Hourglass. And other times, such as in the original game and Links Awakening, the sword upgrade has nothing to do with the plot.
 * Generally, if Ganon's in the game, it'll be the Master Sword. The side-stories substitute their own upgraded blades.
 * The Legend of Zelda: Ocarina of Time is one such game, in which the Master Sword comes one-third of the way through the game's dungeons and triggers a seven-year Time Skip.
 * And the Zelda clone Alundra gives you your initial weapons in this fashion. You need them to solve puzzles just like the items in Zelda games.
 * Ancient Domains of Mystery has the five Chaos orbs which can be worn one at a time for a stat boost, or invoked to use their special powers (at the cost of advancing the PC's corruption).
 * The Vampire Killer in Castlevania: Portrait of Ruin. An unusual case, since the Vampire Killer is A) a whip and B) the hero has it already. The real focus is the quest to unseal it and use it to defeat Dracula, but the hero is warned that if it's used too much it'll kill him the same way it killed his father. There's no ingame effect representing this, but it's hinted it takes longer than one would spend tramping around Castlevania for the effect to kick in.
 * The Masamune from Chrono Trigger is an interesting case. It's required to advance the plot, but since it's just used at the halfway point, it gets overshadowed fairly quickly by other weapons Frog can just buy. However, one sidequest can empower it to its full potential, making it both this and an Infinity+1 Sword at different intervals.
 * The titular Crystalis, though you acquire it right before the final boss battle, after entering the Point of No Return.
 * The titular Daikatana.
 * Yeah, though most people couldn't even find the sword for about three years.
 * And once you did, it was less useful than a gun...although more useful than your sidekicks.
 * In Doom 3, on your first journey through Hell, you find the "Praeleanthor", a.k.a. "The Soulcube". It was apparently being used as a portal between Hell and Mars, but it also functions as a weapon that can one-shot every non-boss enemy in the game, including the Vagaries and Hell Knights. It's also the only way to kill the Cyberdemon, the only creature you will find that can withstand multiple Soulcube hits (or any at all, besides Sabaoth).
 * Erdrick/Loto's Sword in the original Dragon Quest and next two sequels. The Zenith Sword in IV through VI, though with a different name and color in the last.
 * In Dragon Quest III, an astoundingly significant portion of the game is spent trying to get the Gaia Sword, just so that it can open a path to a MacGuffin.
 * This sequence involves getting a ship, finding a place you can't go with the ship, finding a mirror that you can use to get a staff that you can trade to get a bone that you can use to get a locket that you can use to unlock the place you can't go with the ship. If you're following the manual, this will take you from level 20 all the way to level 34, in a game which recommends you be level 40 to fight the end boss. And that's just to get the Gaia Sword. The only purpose of the sword is to get you to the last of six orbs, five of which you picked up while trying to get the Gaia Sword. Ugh.
 * You open up the path to the last orb by throwing the Gaia Sword into a volcano. There aren't even any bosses between getting it and getting rid of it.
 * And in Dragon Quest IV, there's an entire set to collect, with the Zenithian Armor, Helmet and Shield to match the inevitable Sword.
 * In Dragon Quest V, you are required to do two long dungeons and marry a girl in order to get a plot-advancing shield...and you can't even use the damn thing until later in the game.
 * Justified:.
 * Despite not being a tangible object, the great power that Ness discovers in himself near the end of EarthBound fits this trope.
 * Ecco the Dolphin receives the power to Advance the Plot from the Asterite in the penultimate sections of the first and second games. The fact that it eliminates the need to breathe is a small bonus.
 * The Elder Scrolls III: Morrowind has the hammer Sunder, the sword Keening and the gauntlet Wraithguard that you need to use together to defeat Dagoth Ur. Interesting thing is that they don't need to be used against him personally. You're supposed to strike the Heart of Lorkhan once with Sunder and then three times with Keening to kill him.
 * Its expansion Tribunal not only asks you to find but to repair and relight (yes it is a flaming sword) the blade Trueflame. It's important to the plot. Really.
 * It is important to Almalexia and getting her to reveal the fact that.
 * One of the people who help you restore the blade points out that the flames are pretty much for decoration, and have absolutely no effect on its performance as a weapon. Looks pretty, though.
 * It is still a pretty powerful weapon. It is the most powerful artifact sword in the game. This means that it lacks the massive enchantments that are possible with player enchanted weapons. It does only 30 fire damage as opposed to the 300 possible with a top level sword and soul gem, as well as having a slow swung. It is one handed though which allows one to use a shield, which is at the very least an additional enchantment slot.
 * Having a weapon do 300 magic damage sure can suck when you meet high level enemies that reflect/absorb magic.
 * An Elder Scrolls Legend: Battlespire has the Moon Reiver, the only sword that can hurt the final boos, Mehrunes Dagon.
 * The Sword of Aeons in Fable if you're evil, or Avo's Tear if you're good, although Avo's Tear only appears in the expanded re-release of Fable. This should be in 'infinity + 1 section as you get it after you beat the game and no enemy demands it to be killed.
 * It averts the Infinity+1 Sword territory in the expanded Lost Chapters version of the game, since you easily have 5-10 hours of remaining gameplay to go through after you acquire the swords. And since a quarter of the game was spent attempting to stop from acquiring the blade, it is still plot relevant. Lost Chapters also nerfs the Sword Of Aeons (and introduces Avo's Tear as its counterpart).
 * Also the in Fable 2 sort-of becomes this trope, although its not really a sword, and
 * Scimitar of Baron slaying +3 anyone?
 * The Ultima spell in Final Fantasy II.
 * Final Fantasy IV has Cecil receive the Legend sword (or Mythgraven sword, for the remake) when he becomes a paladin.
 * Though it can eventually be reforged into the Excalibur, second (or third, depending on the version) best sword in the game.
 * Also, the twelve legendary weapons in Final Fantasy V. For the last portion of the game, Ghido entrusts you to collect four tablets in order to unseal the weapons, three at a time. Almost averted, as the weapons are incredibly powerful and yield neat bonuses when you equip them. However, the final dungeon includes even more powerful weapons, so much that most of the legendary weapons are overshadowed. The ones that don't? Weapons you wont ever use, like bells and whips.
 * Crisis Core: Final Fantasy VII has Zack obtain the almighty Buster Sword after It doesn't do anything to his stats, but its acquisition is absolutely necessary mandatory.
 * Interestingly, by the time of Final Fantasy VII, the Buster Sword is Cloud's weakest sword.
 * Final Fantasy XII gives you two such swords, with opposite functions, and a major part of the plot is the heroine deciding which sword to use. They have the exact same stats in battle, and completely suck.
 * In fact, the only reason you would ever use one of them is on a Self-Imposed Challenge, as they are the only weapons in the game that don't require licenses to use.
 * In the first Fire Emblem game, a lot of the plot is involves Gharnef stealing the Falchion early on and Marth reclaiming it near the end of the game. Of course, due to the early game mechanics, it's entirely possible to skip out in getting it and finish the game without it. Its advantages are infinite durability and effectiveness against dragons, but in terms of power there are several weapons that overshadow it...which you get earlier on.
 * In the Fourth game, there's Tyrfing. You hear a couple passes at this Legendary Sword in the first generation, but nothing important, then early in Chapter 5, you're given it-- and it's quite powerful, but you don't have it long for certain reasons  Come Chapter 6, however, which starts with the main character's son, Celice- Tyrfing has become this- an all important sword that will make Celice a Badass that can kick The Empire in the nuts, once he gets it, that is. Unlike most other examples however, this IS Celice's best weapon. (And like the Falchion, it's possible to miss Tyrfing both times).
 * Forgotten Realms: Demon Stone has the silver sword of the Githyanki, which is needed to kill the Slaad Lord.
 * Grandia II features locating the Granasaber, a sword that fell to earth during a battle between two Gods, as a major part of the game's second act.
 * There's also the Spirit Sword of the original Grandia.
 * Lufia and the Fortress of Doom and Lufia: the Legend Returns have the Dual Blade, a sword wielded by the hero's ancestor, Maxim, which is the only weapon capable of harming the deity-like Sinistrals terrorizing the world. A substantial portion of both games revolve around mounting an expedition to recover this sword from the site of your ancestor's final battle.
 * In the prequel, where you play as Maxim, he proves his worthiness to wield the Dual Blade by forcibly taking it from the Big Bad himself near the end of the game.
 * The Sword of Mana in many of the Mana series of games. It often has rusted or the like over the years, and requires repairs through the course of the plot. Sometimes these are incremental, and sometimes these happen all at once. The final repair inevitably turns it into the Infinity+1 Sword.
 * Strangely, in some games (Sword of Mana, Legend of Mana, Seiken Densetsu 3) in the series it can never be equipped.
 * And Children of Mana...come to think of it, is there any game other than Secret of Mana and the original Final Fantasy Adventure where it can be equipped?
 * Even in Secret of Mana, while the sword you equip is the Sword of Mana, it does not become the Sword of mana until magically imbued by your teammates during the last battle, or through a glitch. Otherwise the best you can use is the next level below.
 * Basically in games where you can wield it, you only get the sword literally 5 seconds from or already engaged in the end fight. In installments where you gain it earlier, nobody—including heroes who look tailor designed for the role—is smart enough to pick it up as a weapon. Not even in the game named after the sword.
 * Which, according to the series's Japanese name, would be every game.
 * In Secret of Mana, you have the Sword of Mana from start to finish. Even if its not at full power, it is still the Sword of Mana, no other sword can replace it.


 * The Sword of Gith in Neverwinter Nights 2.
 * Regaining the now even better Sword of Gith in the Mask of the Betrayer expansion.
 * About three-quarters through the Xbox Ninja Gaiden and the Xbox 360 Ninja Gaiden II, Ryu gets to combine the Dragon Sword with the Eye of the Dragon to form the True Dragon Sword that is supposedly needed to defeat the Big Bad.
 * Orakio's Sword in Phantasy Star III: Generations of Doom.
 * And Elsydeon in Phantasy Star IV: End of the Milennium; with the bonus multiplier against Evil-type creatures and a chance of getting the 'Holy Word' effect, this also makes it the Infinity+1 Sword.
 * Two easier-to-miss ones, also from Phantasy Star IV, are the Eclipse Torch and the Psycho Wand. The former is used to burn away evil trees blocking your path, and the other was needed to break The Dragon's otherwise impenetrable barrier. The Torch can be used as a Holy attack item in battle, and the Wand can be used to break barriers on the few enemies that use them, throughout the entire game.
 * The boxart-featured Mons (Groudon, Kyogre, and Rayquaza for Pokémon Ruby and Sapphire and Palkia, Dialga, and Giratina Pokémon Diamond and Pearl) must be encountered to advance the plot (though Rayquaza doesn't have to be fought right away; it only needs to be approached), though this only applies to the one on the box of the game being played. Suicune from the second generation was like this as well (again, only for the game it appears on the box for, in this case, Crystal). The ones from the other second generation games (Lugia and Ho-Oh) become this in their fourth-generation remakes (which add a Suicune subplot as well), despite being optional except for One Hundred Percent Completion in the original versions of the games (the one on the box of the game being played could merely be encountered earlier the original versions of the games, with the other game's mascot being available later).
 * And in Pokémon Black and White, you are  in order to defeat.
 * In the Realmz scenario Assault on Giant Mountain, you must acquire the powerful greatsword Giant Slayer in order to proceed...but the reason it's necessary isn't so that you can wield it, but because the Big Bad's fortress is magically inaccessible until you destroy it on the Anvil of Pain. This is difficult to do since it's probably become your fighter's favorite weapon.
 * This trope pops up in other scenarios too, like the obsidian scimitars from Destroy the Necronomicon and the Spear of Light from Griloch's Revenge.
 * In SaGa 3 The Mystic Swords are the only weapons capable of damaging the Big Bad
 * Shadowkeep required you to find the Black Sword, the only weapon that could harm the evil overlord (and another item, the only thing that can keep him from killing you in one blow.)
 * In Shining Force you combine the Sword of Light and the Sword of Darkness to make the Chaos Breaker.
 * Shining Force II has both the Achilles Sword and the Force Sword (which, as revealed in Shining Force Gaiden: Final Conflict, is the Chaos Breaker mentioned above, just renamed). Oddly enough however, in the second game it looked more like a lightsaber (get it?).
 * Shining Force The Sword of Hajya has the titular sword be required to deal the first swing to the Big Bad.
 * In Shining Force II the Achilles Sword is Exactly What It Says on the Tin in a way that will become extremely obvious once it happens.
 * The "Force weapons" in both Star Ocean and its sequel, though their importance to the plot is only revealed just before you get them.
 * Happens all the time in Super Robot Wars, and sometimes inverted when its a machine you have to destroy. Memorable examples include Ryukooh and Koryuoh, Getter Shin Dragon from SRW Destiny, the R-Series in Original Generation 1 and the enemy unit Judecca.
 * The Eternal Sword in Tales of Phantasia and Tales of Symphonia. In other games it becomes the Infinity+1 Sword
 * The Key of Lorelei in Tales of the Abyss.
 * Dein Nomos in Tales of Vesperia is a slight subversion as you get it about 2/3 into the game, it's far from being Yuri's ultimate weapon and you lose it after a few dungeons. In the PS3 version
 * Wahrheit in Tales of Hearts - after it's been converted to the Global Airship Lianheit. (It's the personal weapon of a nonplayable character.)
 * in Tomb Raider: Legend. You only get to use it for a brief escape scene and a boss before the game abruptly ends though.
 * In Underworld, you also get your hands on.
 * The original Black Sword in Ultima VII. Or the Mystic Arms in Ultima IV.
 * The Black Sword is only needed to complete the Forge of Virtue expansion, not the main game. Since the expansion is entirely optional, this may not count. Also, you don't need the Mystic Arms to complete Ultima IV. The game claims only Mystic Arms work in the Stygian Abyss but in fact any magic weapon will work.
 * In VII part 2 (The Serpent Isle), you start the game with the sword (implying the Avatar did complete the Forge expansion), promptly lose it, and need to recover it in order to get packed off to the world of Pagan.
 * The Sword of Justice from Ultima Underworld probably counts, as it's one of the 8 items needed to complete the game and is a very good weapon (the only unbreakable one as well). Subverted in that completing the game requires you to destroy the sword (along with the other items). Trying to kill the Big Bad with it is pointless.
 * In Unlimited Saga you have at some point to collect the elemental gears in Laura's quest, some of the best equipment you'll ever get in the game.
 * The title sword in the first Vandal Hearts; in the sequel, it is optional for the overall game, but necessary for the best ending.
 * The Runeblade Frostmourne from Warcraft 3 is vital to freeing the Lich King, but also grants a combat boost when Arthas first gets it. Annoyingly, this boost goes away when you start the next campaign, and from the on its power is only shown in cutscenes, though it theoretically responsible for Arthas' death knight powers as well.
 * The Mavin Sword in the D.W. Bradley game Wizards & Warriors, acquired just before the third act of the game, and it's quite a powerful sword, in addition to supposedly being the only weapon capable of harming the Big Bad (there's actually a second weapon able to harm the Big Bad, not that you're ever told it can do so).
 * Happens twice in Zeliard. The Knight's Sword is the first sword that's (at that point) only available as a 'quest' rather than simply buying as an upgrade, and you're told it's essential to beat that level's boss (apparently, overly keen players have showed that it's not). Near the end, you're supposed to find the Faery Flame Sword in a fairly similar manner.
 * The Gears and Omnigears of Xenogears are required to fight many bosses and complete many dungeons. Citan's sword, cool as it is, is not all that plot-relevant.
 * In the original Devil May Cry, after Dante defeats the Black Knight Nelo Angelo for the last time the knight drops an amulet, identical to Dante's own. Anyhoo, the amulet combines with Dante's into the Perfect Amulet, which is part of the way to open a Portal to Mundus's world as kick his ass. Additionally, exposure to the amulet unlocks the true power of the Force Edge, Dante's starting sword; it becomes much stronger as Sparda. The Sparda is the only weapon Dante can use against Mundus's first two forms anyways.
 * Rogue Galaxy does the first type TWICE and the second type once: An equippable weapon crafted from plot coupons in the penultimate dungeon, which goes away after the first two of ten final boss battles, a Blade of Fearsome Size Jaster automatically gains and equips for the VERY final battle, and the Desert Seeker Jaster gains at the beginning of the game (which can evolve into one of his strongest weapons, making it the second type).
 * The titular Valis Sword.
 * The Firestaff in the Deus Ex mod "The Nameless Mod". It's not really a sword (it sets things on fire instead), but it has administrative powers and thus is very important to the plot.
 * In Black Sigil, Kairu is entrusted the Sword of Averay by his adopted father, Duke Averay. It eventually becomes critical to the plot involving the Sealed Evil in a Can.
 * The first Gothic has the sword Urizel, which is one of the few things that can harm the last undead orc shaman. (Spellcasters can have it turned into the "Wave of Death" rune, which is the only other thing capable of harming said enemy.) Note that you find it well before the end of the game (and have to empower it in a spectacular fashion), so you get to enjoy its sheer killing power on many regular enemies as well. In a more strict interpretation, you have to obtain the shamans' five swords, which are too damaged to be of regular use, but are vital to defeating the Big Bad right at the end.
 * Wild ARMs 2 has the Argetlahm, which subverts this trope before playing it straight. Its first appearance makes it obvious that you won't obtain it until the end of the game, but you're quickly forced into a situation where it's absorbed by the hero to turn a Demonic Possession into a mere Super-Powered Evil Side.
 * The Silver/Cleria Sword in Ys I and II. In Book 1, you get it right before The Very Definitely Final Dungeon, and there is an Infinity+1 Sword in said dungeon, but that doesn't work against Dark Fact. In Book II, it is the Infinity+1 Sword, and you obtain it just before fighting the Big Bad Darm. In Ys IV: The Dawn of Ys, you start with the Cleria Equipment, but lose it shortly after, to regain it near the end of the game. Ys: The Ark of Napishtim, the sixth game in the series, has only three swords (which can be upgraded) and all of them are relevant to the plot.
 * Leo's Sword (that's the name of the sword itself) is this in Record of Agarest War. Seemingly only used in cut scenes, when you  Makes you wonder why you could not use it in gameplay even though Leo has it in his hand and could have prevented his death all the way back from the start.
 * Golden Sun: Dark Dawn has the Sol Blade, which is required to . It's also used to access certain dungeons.
 * The Ultragunner in Vanguard Bandits.
 * The Dragon Slayer in Legacy of the Wizard and Faxanadu.
 * The Hawke's Key in the Dragon Age II "Legacy" DLC. You obtain it fairly early in the quest, and it is vital to progressing through the dungeon. Since it's leveled like most of the equipment in the game it will be powerful when you get it but it will be eventually obsolete.
 * In Mantra, the main plot coupons (the eponymous five Mantras) are magic scrolls. Each one gives you the ability to perform a specific type of attack that has an elemental damage type. They're useful in combat with normal enemies and bosses, and they're also necessary to destroy barriers which are only vulnerable to specific elemental damage types, so that you must acquire the appropriate Mantra in order to advance to the next area.
 * The Monado from Xenoblade. Almost everything in the game's plot is done in to, by, or in response to it.
 * The Magic Sword in Hyperdimension Neptunia mk2 where it has been said that it can demolish the most powerful evil in existence. There's just one problem.
 * Splendor in Deadly Towers.
 * The Lord of the Rings Online introduced a system of Legendary Item advancement in its first expansion, Mines of Moria. Until the player receives his Legendary weapon and proves that he can operate with it (reforge, slot relics, apply titles etc) he cannot advance the Main Storyline and cannot pass the Doors of Moria.
 * An example from the original book is Narsil / Anduril. Turns out a special mineral is required to reforge such an epic sword and the player is send on a quest to get a piece of it (which composes the longest non-epic quest chain in the game by the way). Until you finish it, Narsil cannot be reforged and the Fellowship cannot leave Rivendell.
 * Fallout: New Vegas features this in the Old World Blues expansion - the Think Tank wants you to collect three items to defeat Dr. Mobius - a frequency to disable force fields, an antenna to amplify the frequency, and a stealth suit to sneak into Dr. Mobius's lair.  That said, even after the quest, all three items are quite useful when exploring the Mojave.
 * One of the last things to do in Might and Magic VI before attacking the Kreegan Hive is to acquire blasters and the skill to use them. Unusual in that there are several blasters to be found in the associated dungeon, significantly more than the four characters you have, and in that there are upgraded versions deeper in the dungeon that count as blasters for all important purposes, but they can only be found in that dungeon, and getting at least one is absolutely necessary to finishing the game (for more than one reason if you want to finish the game without a Nonstandard Game Over)
 * One of the last things to do in Might and Magic VI before attacking the Kreegan Hive is to acquire blasters and the skill to use them. Unusual in that there are several blasters to be found in the associated dungeon, significantly more than the four characters you have, and in that there are upgraded versions deeper in the dungeon that count as blasters for all important purposes, but they can only be found in that dungeon, and getting at least one is absolutely necessary to finishing the game (for more than one reason if you want to finish the game without a Nonstandard Game Over)

Film

 * In Star Wars Episode IV, receiving his father's lightsaber is part of Luke's Call to Adventure near the end of act 1.

Literature

 * The orb of Aldur from The Belgariad seems like a MacGuffin until the hero picks it up near the end of the series and starts whomping all kinds of ass with it (and his signature Blade of Fearsome Size, of course, which is so heavy that the orb has to "carry" it for him). In the follow-up series it is more the first type, since he already has it, but it becomes useful in all kinds of other ways throughout.
 * Considering the sword was forged from two fallen stars, it was enourmously heavy. The original creator was even advised to remember the weight, because if the orb were removed, and he were holding the sword, he'd likely break his wrist.
 * In The Wheel of Time the one who can wield the crystal sword Callandor is the Dragon Reborn - the chosen one. The main character acquires it in the third book and then announces his station to the world.
 * "The only one who can wield it is not precisely true. He was the only one who could pick it up without dying, yes, but as soon as he did, the magic protecting it was gone. After he left Callandor behind at the Stone of Tear, Morgaine berated him for leaving the third most powerful magical object in existence lying around for his enemies to steal.
 * Of course that's expressly NOT a sword.
 * Really, it is a sword, being sword shaped and sharp and fully capable of being used as a sword. It's just that it's also such a strong Amplifier Artifact that using it as a sword is a complete waste of of its potential.
 * Harry Potter and the Deathly Hallows is focused on Harry, Ron and Hermione's trying to find/destroy Voldemort's Horcruxes. The quest only takes off after they discover where Gryffindor's sword is hidden.

Mythology

 * King Arthur getting the Sword in the Stone and Excalibur (which may or may not be the same - Arthurian canon can be confusing) are important steps in his rise to power, and Excalibur is his main weapon through pretty much the entirety of his life.
 * In Norse mythology, Siegfried (or Sigurd) pulling the sword Gram (or Balmung or Nothung) from the tree into which Odin had stuck it.

Video Games

 * The second Golden Sun game has a weapon of plot advancement., that stays relatively useful even after picking up the Infinity+1 Sword.
 * Due to the fact that said weapon isn't really a weapon, but rather an accessory that stacks with everything else. Hey, free 10 Mercury Resist so why the hell not?
 * The Keyblade from Kingdom Hearts, which changes its outward form and power throughout the game but has essentially the same plot-important abilities. It's also an Empathic Weapon.
 * Raziel gaining the Soul Reaver following the second boss-battle of Legacy of Kain: Soul Reaver.
 * In Heavenly Sword, the eponymous Heavenly Sword.
 * The Prince gaining the Dagger of Time early on in both The Sands of Time and The Two Thrones, allowing access to the time control gameplay that is the series selling point.
 * In an interesting partial subversion, you generally get the weapon very early in these games (or start with it) and the idea is to get rid of it properly.
 * Another interesting point about The Sands of Time is that you actually get to use the Infinity+1 Sword for awhile (after ) that can shred enemies in a single blow without having to absorb them into sand (though you do lose your time flipping powers in the process so it waltzes between this Infinity-1 Sword status). However, the end of the game and you're stuck to using your original weapon (the one you started with) and the Sword of Plot Advancement again for the final battle.
 * In Warrior Within the Prince finds several of these: the Serpent sword which acts as a key granting him access to certain areas of the fortress, later the Scorpion sword, which can break through walls and will be used in something of a hail Mary plan, and finally the alternate-ending-providing Water Sword
 * The sword in level 8 of Prince of Persia 2: The Shadow and the Flame has a cutscene of its own. It replaces the clumsy dagger you've been stuck with ever since you lost your old sword a few levels back.
 * The lightsabers in some Star Wars games, usually coupled with Force powers. Acquiring/building a lightsaber typically marks the transition from a mere Mook to a full-fledged Jedi, in other words, getting ten free levels in badass. This is when the real fun usually begins. Examples: Jedi Knight II: Jedi Outcast, Knights of the Old Republic.
 * The titular Sigil in Strife: Quest for the Sigil. It's the only weapon which can hurt bosses (well, a particular kind of boss). It's also an Evolving Weapon.
 * Not technically an Evolving Weapon - there is actually assembly involved. You just don't see it unless you're paying attention because pieces of the weapon automatically fly to you and self-attach when the enemy carrying them is defeated...even if you'd prefer they didn't.
 * The Ultimate Legedary Epic Weapons in Kingdom of Loathing are upgraded from your Legendary Epic Weapons right before fighting the final,  form of your Nemesis. Their lesser forms are neither the first or the second type, but the Legendary Epic Weapons are arguably the second type of Sword of Plot Advancement.
 * The Armageddon Blade in Darksiders. The last weapon you get - however arguably not the most powerful.
 * Despite other examples of the same weapon being type 1 in most other games in the Zelda series, the Master Sword is type 2 in Wind Waker and Twilight Princess. This is particularly the case in the latter title, as acquiring it lets you transform into a wolf at any time, as well as use the game's warp system.
 * Skyward Sword really runs with the idea; near the start you get the Goddess Sword, which fits for second type on its own; however, other Plot Coupons you pick up during the game make it stronger, eventually turning it into.

Web Original
"Church: "So it is a sword. It just acts like a key in certain situations." Caboose: "Or, it's a key all the time, and when you stick it in people, it unlocks their death.""
 * Tucker's Plasma Sword in Red vs. Blue. It starts out as a cool sword that can only be used by the "Chosen One", who is also the most evil (and/or stupid) individual in the universe (leading to a Crowning Moment of Funny where Church names Caboose as The Antichrist). When it's taken to the frozen northlands, it can be used to unlock and power up a Cool Ship. It also gets a little philosophical when deciding wether it's really a key or a sword.

Anime and Manga

 * In an odd manga example, the Ten Commandments Sword from Groove Adventure RAVE, is not only obtained early and one of two driving forces behind the main character's powers and abilities, but powers up not once, not twice, but NINE separate times. The last of these power-ups results in Ravelt, a Sword of Plot Advancement in its own right.
 * Utena is able to draw the sword of Dios from the Rose Bride starting in episode two, marking the beginning of her journey as a duelist. For the first arc of the series, this fantastic element seems fairly self-contained to Anthy; starting the second Black Rose arc, everyone can pull swords out of other people's chests! This ultimately culminates in Anthy having to draw a sword from Utena's breast, since Utena can no longer draw the sword of Dios from Anthy: Anthy draws the sword of Dios. As a bonus, these "soul swords" not only represent plot advancement (even if Utena can't see it) but also reflect character development and dynamics.

Live Action TV

 * Several Heisei Kamen Rider series have the main character gain his Super Mode via the acquisition of a unique and powerful sword, hence the Fan Nickname "SwordGrade" (sword + upgrade). Examples include Faiz's Faiz Blaster (doubles as a BFG!), Hibiki's Armed Saber, and Den-O's DenKamen Sword. Kabuto's Perfect Zecter and Kiva's Zanbat Sword are typically counted despite coming after the Rider got his Super Mode, while Agito Shining Form, Blade King Form, Double CJX, and OOO PuToTyra have swords (or in OOO's case, an axe) that are part of their powers, rather than the source of them.

Role Playing Games

 * In Dept Heaven Apocrypha, Monica's legendary sword Joyeuse is technically her Call to Adventure proper (and thus signals the First Act); learning to use it will be another matter, and once it's mastered her plot will move to its second act.

Video Games

 * The Soul Reaver falls under both categories, as it basically drives the whole plot in the series. As mentioned above, it falls under the second category in the second game, in that Raziel gains it early in the adventure and it's a defining ability in the subsequent games. It falls under the first category for how late Kain gets it in the first game, and how it's the linchpin of how to see and defeat in the last game.
 * Frostmourne in Warcraft 3 starts as a Type 1, signifying the last stage of the human campaign and giving Arthas the power to destroy Mal'Ganis. It then becomes a Type 2, when it also initiates the second act of the game as a whole - the undead campaign. Although at this point it loses any effect on game mechanics, and displays its power only in cutscenes.
 * The Epic Weapons (and their more powerful forms, the Legendary Epic Weapons) in Kingdom of Loathing are actually neither of the types, but still Swords of Plot Advancement. The Epic Weapons and the Legendary Epic Weapons are gained in the middle of the quest to defeat your Nemesis (for the first time). The Ultimate Legendary Epic Weapons, on the other hand, are the second type of Sword of Plot Advancement.
 * The Blade of Olympus in God of War 2 drains all your power from the first game and you spend the whole game searching for a way to retrieve it from Zeus' grasp. When you finally do, it's your main weapon in the boss fight with him.
 * Tactics Ogre: Knight of Lodis has Longicolnis. Being a spear, it has some useful range advantages, can hit multiple enemies at once, gives bonuses to Virtue and Bane resistance, and unlike other spears doesn't have any movement penalties. However, there are a few weapons, aquired both before and after it, that are more powerful, though you still need it because you won't be able to harm the final boss without it.

Webcomic

 * The Sword of Xel Dum is a great example of this from the NSFW webcomic locus has a curse that requires the central character to kill whoever tries to take it for her, including the original owner....that's some plot advancement.

Visual Novels

 * The black sword acquired by halfway through Shikkoku no Sharnoth.