Evolving Weapon

Just as characters can get stronger by killing things (leveling up), so too can their weapons. Absolutely no modifications are made to the weapon, they just get stronger by killing things. Which makes no sense without some kind of Applied Phlebotinum at work. Is occasionally handwaved that the weapon has a sort of vampiric nature, or that killing a certain creature for so long has made it more effective against them.

In fairness to this trope, there are some good reasons for it. Having a evolving weapon allows the hero to carry it throughout extended lengths of gameplay without the weapon becoming obsolete and underpowered compared to your hero, thus making it a bit of a trademark of the hero and highlighting how awesome it is. By unlocking its powers bit by bit, you also avoid having a too good weapon early on.

Alternatively, there is a second way this works. Instead of the power gain being permanent, sometimes it is only temporary. Maybe it unlocks some of the weapon's hidden abilities, or there might have been something special about what was just killed. Subtrope of Empathic Weapon.


 * In Fable III, the first weapons you got are evolving weapons (It's not even a secret) that change depending on what you've done before upgrading the skill (Ranged changed your gun). So every player ends up with a unique weapon by the end of the game.
 * Wrath of the Lich King brought the joy of heirloom-type items to World of Warcraft. While the weapons and armor themselves don't grow because of their being used, they still count as Evolving Weapons because they scale to the character's level. This also means they can be recycled and can be used from 1 to 80 before being tossed onto another alt.
 * Go back one expansion, to The Burning Crusade, and you find a series of Blacksmith-crafted weapons, each of which can be upgraded twice to a more powerful version. Example: Lunar Crescent -> Mooncleaver -> Bloodmoon.
 * In Final Fantasy X, the sword Wakka gives to Tidus upgrades automatically when the party visits the Farplane, and Wakka is seen talking to the sword's former owner.
 * Also, all of the Ultimate weapons in Final Fantasy X are upgraded twice, once by finding a relatively easy key item to find, and again by finding a very difficult to obtain key item. They upgrade from Useless weapons which completely stop experience gain, to swords with an ability which also stops experience gain, finally to a weapon which breaks damage limit for both the character and Yuna's associated Aeon (summon) for them for no particular reason, increases experience gain and has several other abilities depending on the character (One MP cost for Lulu, Counterattack for Tidus etc.)
 * In addition, the final form of each ultimate weapon has a hidden ability, which increases the attack power of the wielding character depending on a certain condition (it depends on the character).
 * The Atma Sword in Final Fantasy VI has an attack power that is a function of the Hit Points of the character wielding it. As they get stronger, so does the sword.
 * Vincent's Death Penalty gun in Final Fantasy VII does more damage with each enemy it kills. Kill about 65 thousand or so, and it'll glitch out and kill anything in one hit.
 * Conversely, the Tonberry's Knife/Grudge attacks in the Final Fantasy series have the enemy attack get stronger with each kill your characters make.
 * The Sequencer in Final Fantasy Tactics A2 gets more powerful each time you get an Opportunity command.
 * The Dragon Slayer from Berserk has become an anathema to Demons thanks to Guts relentlessly killing them for three years.
 * Inuyasha's sword, Tessaiga, explicitly has the ability to get stronger by killing things and gaining related abilities.
 * Another Inuyasha villain had a weapon that gained demonic power after killing 1000 humans and 1000 demons.
 * Pins that Neku uses in The World Ends With You will sometimes evolve if you kill enough Noise, or have on him while the DS is off or in mingle mode. You're never informed which needs which.
 * In both of the Dark Cloud games, weapons are leveled up by killing monsters with them. Many weapons can also literally evolve if you got their stats high enough.
 * The Muramasa in some Castlevania games will gain attack power as you kill enemies. Something about the sword being cursed and having to drink blood.
 * The Muramasa puts Alucard in permanent "Dark Metamorphosis" mode; meaning that he recovers health by touching the blood of enemies. The more blood he absorbs, the stronger the sword gets. As such, killing a skeleton won't do anything, but killing a merman will.
 * This is basically the entire premise of Soul Eater.
 * Looking at what the Weapons can do to witches in the hands of meisters allied with Shibusen, one wonders what exactly Arachne was thinking. The 'Heretic' not only killed her fellow witches For Science (used the Book of Eibon to put into practice something that had never been done...for no clear reason), but gave one willing to wipe out almost her entire race for his own sense of justice (Shinigami might have fair reason, but his methods are questionable) a really effective way of doing so.
 * It occurs before the timeline of the games, but Soul Edge from the Soul Calibur series of games began as a normal sword, and eventually gained its demonic nature by being bathed in the blood of countless victims.
 * The Devil's Arms in Tales of Symphonia which have their attack power based on killcount.
 * In the PSX version of Tales of Destiny, some of the characters have Swordians, special swords with personalities that can talk. They gain EXP along with their owner, and can level up to get stronger and learn new spells for their owners to use. While all the Swordian Masters of the party have other weapons that they can use, the spells and evolution of the Swordians tends to make them the weapon of choice.
 * In addition to the Devil's Arms present throughout the Tales (series) the Sorcerer's Ring is this in Tales of Vesperia. Over the course of the game higher levels of aer(read magic) will make it shift and become stronger. The plot only requires it to get to level three but to complete the Devil's Arms sidequest it has to get to level five.
 * Every weapon used in the Ratchet and Clank series from Going Commando on, and in the Challenge Mode of the first game, if you've collected enough Gold Bolts.
 * The Speculative Fiction novel The Practice Effect has a world where all tools follow this trope. The hero is from "the real world" and figures out that already well-made items from his world have a huge headstart.
 * Very unusually for this trope, devolution is in full effect; any man-made object is slowly shifting into a less usable form the longer it goes unused. This means it's very difficult to maintain anything not made for a single specific purpose in its full condition. It also causes problems with higher technology, due to the intolerance of electronic components to slight physical changes and degradation. Most of the (rather well-prepared) hero's equipment is entirely useless within a week. Even his Robot Buddy, who never turns off and so counts as always "practicing" itself, tends to lose functionality not related to executing its immediate instructions.
 * Secret of Mana
 * Retro Mud has the Fellblade, which is essentially this.
 * Weapons in GunHazard work like this. So do the verniers. And the armor plates. And the Wanzers themselves (Wanzers and armor actually gain EXP by being hit).
 * Weapons in Cave Story can be leveled up by killing enemies, indirectly. The enemies drop little triangles which can be collected to level up your weapons. On the other hand, getting injured can de-level the weapon you're using. It's inverted for one powerful end-game weapon which gets weaker when leveled up, so you have to avoid collecting energy triangles while wielding that weapon. Considering you've now got half a game of muscle memory telling you to grab the triangles, that's not so easy.
 * Averted with another end-game weapon, as you don't have to level it up. It's always at the max power of the Polar Star (the gun you get at the beginning of the game) no matter what you do, but you CAN hold the shoot button and level it up to max (it doesn't level up like any of the other guns, surprisingly) for a supremely powerful laser burst.... Not that you'd need it.
 * Fusion and Lumina from Brave Fencer Musashi. Each of them gradually gains strength whenever Musashi uses them to attack, and this is separate from his own strength stat. Fusion is also of the second type, as noted below.
 * Psyphers in Odin Sphere gain strength by absorbing Phozons, small bits of life force released whenever a living thing dies.
 * The Solar Gun Lenses in Boktai: The Sun Is In Your Hand inexplicably gain levels up to III by killing things with them equipped.
 * The titular Daikatana gains levels if you use it and becomes deadlier and faster. However your character doesn't gain any experience points this way and does not get to raise his stats.
 * Raidou Kuzunoha can visit affable Dr. Victor to reforge his swords: in the first game, he will fuse a demon into the sword, granting it powerups based on the demon's level and abilities, and in the second, a special crystal will be fused into the sword, changing its attributes depending on the used crystal.
 * The Sealed J-Sword in Phantasy Star Online. Normally a semi-decent weapon that inflicts serious status ailments on you, with enough kills with it equipped, and it will evolve into one of the most powerful weapons in the game.
 * Dak'kon's zerth blade from Planescape: Torment, which levels up at the same time he does, being a weapon made of karach, a material of pure chaos that mirrors the mind of its owner. It's referred to in dialogue as something that could become powerful enough to destroy the multiverse itself if fueled by enough will and determination, and while you never see it do anything quite that impressive, it can end up a pretty neat weapon if Dak'kon is in your party right up until the end game. It also can become weaker if you deliberately plunge Dak'kon into doubt and emotional disarray, or become even more powerful by strengthening his belief in the Unbroken Circle, the philosophy he follows.
 * Ingress' teeth can also evolve if you ask them nicely, eventually becoming magical of their own volition and adding weapon enchantments.
 * Blood Rayne's Carpatian Dragons in Blood Rayne 2 are of vampiric nature, and level up through use, to an extent. Simply firing them improves their power and blood capacity, and they also acquire more powerful modes after defeating powerful vampires/dhampirs, even if they aren't used through the entire battle.
 * The Chicken Knife in Final Fantasy V gains an attack point for every time the party has fled a battle. It can easily become the strongest weapon in the game.
 * The same game contains an inversion in the Brave Blade, which decreases in power every time the party flees a battle, essentially making it a devolving weapon.
 * A borderline example, but the "Dream Sword" weapon in Kingdom Hearts (which can only be obtained outside the "Station" via Game Shark) has an attack power relative to Sora's level divided by 10. If Sora is at level 10 or 20, the Dream Sword's ATK is 1 or 2. But if Sora is at level 100, the swords has an ATK of 10, making it the most powerful weapon in the entire game.
 * In Chrono Trigger, one of the main characters, Frog, gets insanely depressed over a sword called the Masamune. You finally get the weapon, and you would think that that's his ultimate weapon, but no. He has to go and "unlock its true form".
 * Ayla's fist attack also evolves through several types of metal as she gets stronger, each new type giving a new effect.
 * In the Brave Story video game, the main character's Traveler's Sword evolves and takes on new forms whenever he collects certain magical gems (after passing a test of strength and character).
 * Items from Disgaea are a borderline case. They can level up and improve, but only if the player ventures into Item World and subdues the inhabitants inside.
 * The titular Turn a Gundam has this going for it for several reasons. First, Loran uses the instructions manual to find out about all the Gundam's various systems. Two, the grit and grime that was inhibiting its power system gradually falls off, letting the Gundam use its full strength in battle. Three, weapons for it are found over the course of time, causing the machine to change from having a beam rifle that melts after one shot and antiquated maces to powerful beam sabers and a much more reliable beam rifle. And lastly, the revelation about the power of the Moonlight Butterfly and the Turn A's nanomachines.
 * The Lord of the Rings Online introduced Legacy Weapons with the Mines of Moria expansion. Legacy weapons gain XP and level-up independently from their wielder, with some quests even granting Weapon XP as a specific reward. Each level-up grants points to spend on customising various benefits of the weapon, which can also be enhanced by adding special upgrade-items to it. At intervals of several levels, the weapon must be Reforged by a specialised NPC before it can continue to advance. Reforging allows further customisation of the weapon's abilities, increases its base power level, and allows the player to give it a unique name.
 * Magic Knight Rayearth showcases this trope in its first season, in the form of the three main characters' Escudo weapons.
 * In The Shivering Isles, an Oblivion expansion pack, the Dawnfang/Duskfang sword becomes the 'Dawnfang Superior' or 'Duskfang Superior', with additional, life-stealing powers if you've killed 12 enemies with it.
 * Enemies in Vagrant Story have specific types and affinites, and weapons and armor become more effective based on the types of enemies they're used against. Kill lots of dragons with a spear, and it'll gain dragon points that make it more effective against dragons in general. Kill lots of fire-type enemies and it'll become a water type weapon.
 * In Drakengard and its sequel, all weapons can level up. As they level up, all their stats go up (except weight) but their appearance changes and they also explain the history of the weapon with each level up. They can only be leveled up four times and visual change only occurs in the first Drakengard.
 * At least one weapon has good reason for this. It's blade is encased in stone, and as you kill enemies with it, it levels up like everything else. It does this by breaking some of the stone off.
 * In D.Gray-man, Allen Walker's anti-Akuma weapon (his left arm) evolves over the course of the series. At the beginning, it's a gnarly, deformed red arm and all he can transform it into is a giant unwieldy claw. Thanks to a healthy dose of rage and Heroic Resolve, it evolves and becomes capable of transforming into an Arm Cannon and a Laser Blade. After gaining a greater understanding of his weapon and achieving a higher synchronization rate,
 * Diablo II: Lord of Destruction introduced several magic item properties that scale by character level, including bonuses to armor value, damage, and accuracy. Unfortunately, they're rarely worth keeping for very long, as something better will usually drop.
 * Dragon Fable has the Doom Knight equipment set, only available through a cash upgrade, which increases in power every ten levels. At level 60 (the level cap at the time of this edit), the Necrotic Sword of Doom is the best Darkness-based weapon in the game - and its special attack deals 12 hits of regular attack damage, which is easily enough to reduce anything with a weakness to it to a pile of smoking ash.
 * Super Robot Wars Advance has the protagonists' machines, Super Robot Wars Z has the Gunleon, and in Super Robot Wars L, the Rushbird gains new attacks and abilities as the game progresses.
 * Varric from Dragon Age II can never equip any other weapon than his beloved Automatic Crossbow Bianca. Fortunately it levels up with him so it never becomes obsolete. Even better, any rune attached to Bianca also becomes stronger.
 * Various downloads also feature "improve with level up" items, with 1 dedicated accessory per companion, and a few that can be given to anyone capable of equipping them, including weapons.
 * In the third Resistance game, all the weapons upgrade with use. Said game is also made by the creators of the Ratchet and Clank series.
 * The Weapons of Legacy splat-book from Dungeons and Dragons 3.5 is based around this. As you level up and take the appropriate Feats, your Legacy Weapon unlocks more and more abilities of scaling power.
 * In Heroes of Might and Magic VI, playing online allows you to find Dynasty Weapons in the campaigns. If a hero wields said weapons, they gain experience along with the hero. Each weapon has several different abilities that can be unlocked with exponentially increasing amounts of experience, ranging from passive stat bonuses to enemy debuffs/ally buffs.

Examples of weapons with temporary upgrades/changes

 * In The Shivering Isles, an Oblivion expansion pack, there Dawnfang/Duskfang sword transforms between the two forms every dawn and dusk - but if you've killed 12 enemies with it during the preceeding period, it instead becomes the 'Dawnfang Superior' or 'Duskfang Superior', with additional, life-stealing powers.
 * Torg's sword, Chaz, from Sluggy Freelance will become powerful and able to talk once it has come into contact with the blood of a recently deceased "innocent" person.
 * They don't have to be deceased. Alive or dead doesn't matter as long as Chaz comes in contact with the blood of the Innocent.
 * Elric's sword, Stormbringer, will get stronger after killing some poor sap and eating his soul.
 * Stormbringer not only gains strength from feeding on someone's soul, but makes Elric stronger as well (remember he's an albino who previously needed drugs to maintain his strength). Elric's dependence on Stormbringer is an addiction - he tries to kick the habit several times but always finds himself drawn back, until ultimately it destroys him. (However, the comic series Michael Moorcock's Multiverse gives him a second chance at salvation.)
 * The sword "Fusion" in Brave Fencer Musashi has the power to "assimilate" enemies, thereby gaining their abilities. It can only hold one ability at a time; gaining a new one overrides the old one. It is also of the first type, as noted above.
 * In the PlayStation 2 game Shinobi, enemies you kill with Akujiki take a few seconds to actually fall over dead. During this time, Akujiki glows with power and does more damage, allowing to kill more enemies in rapid succession to further extend the time before they die. It is possible to one-hit kill every boss in the game if you kill their minions fast enough first.
 * The fourth edition of Dungeons and Dragons features some magical items -- most notably rings -- with abilities that only become available once their would-be user has reached a 'milestone', i.e. has made it through two encounters without taking an extended rest in between. (Perhaps less directly applicable to this trope, the game also features a limit on how many magic item daily abilities a character can use per day regardless of the number of items available. Each milestone reached extends this limit by one for the current day, thus potentially 'unlocking' item powers that the character could not have used otherwise.)
 * In the Mega Man Battle Network games, there are two Battle Chips (a.k.a. weapons programs useable once per battle per chip) that you can gain, both swords, called the Custom Sword (Cust Swrd) and the Muramasa, respectively, that gain power due to a special condition -- in the Custom Sword's case, its power is determined by the 'custom gauge' at the top of the screen (it can get to around 200 maximum, but when the bar maxes out the power immediately drops to 0), but in the Muramasa's case, it will hit the two panels in front of Mega Man for an amount of damage equal to the HP HE'S LOST. Capped at 999, sure, but 999 in ONE ATTACK (when most Mooks will have phenomonally less, and most bosses hit will lose around or over half their HP) is kind of a big deal.
 * The manga explains this as the weapon feeding off of its user's pain and suffering, which its current user in the manga goes out and gets plenty of -- though one of the more Genre-Savvy members of the Quriky Miniboss Squad (who were all not-so-coincidentally all bosses from the same game) decides to render it all moot by shooting the man in the hands with a Frickin Laser Beam so that he can't hold the Muramasa (what good is an Infinity Plus One Sword if you can't actually SWING it, after all).
 * In Half Life 2 and episode 1, there is a point where the Gravity Gun gets a temporary upgrade and has the ability to lift much larger objects and pick up the combine soldiers to fling them as projectile weapons! This upgrade happens in the end of Half Life 2 and in the beginning of episode 1 where it's only for one area and then it downgrades.
 * In Team Fortress 2, the demoman has a sword that he can use to decapitate enemies. Each head gives the demoman extra health and boosts his speed -- at least, until he dies.
 * Enserric, the vampiric sword in Neverwinter Nights expansion Hordes of the Underdark, gains the ability to drain it's wielder's health to give itself a temporary boost.
 * The Marker in Qix++ can be upgraded in four features using points earned in the stages. It's appearance changes the more upgrades you get. Unfortunately, it's only good in the section you're playing. Start a new section, and you're back to the crappy Marker you started with.
 * In Adventure Quest, weapons and armor gain power the more you level up; weapons increase in base and random damage, and armor in defense and hits of attack.
 * In the light novel and manhua 1/2 Prince, the titular character starts the series with a black dao that can level up with the user.
 * Double Subverted with the Keyblade form the Kingdom Hearts series, while the weapon doesn't grow itself, you can attach various keychains (or gears in days) to it in order to alter it's form and properties such as strength and magic bonuses in (almost) all the games, extra abilities in II, days and Birth by Sleep, attack patterns in Days and Clock gauges in Re:coded. The double subversion in this example, is that the keychains used to modify the keyblade are essentially memories of people and locations used to modify the keyblade's form, the keyblade itself doesn't change, only it's form.
 * Legacy of Kain: Soul Reaver 2 has the named Soul Reaver - remnants of powerful magic sword, fused with protagonist. It becomes stronger when Raziel hits with it. It becomes much stronger, when it consumes a soul of killed enemy. It starts to eat wielder's life when become overpowered. And it slowly returns to normal state, when combat is over.
 * This trooper remembers that named sword was at least in first part of the game and possibly other games of the series, but cannot remember if it has similiar properties there.
 * Skill Cracking in Devil Survivor works like this: you hunt down a demon who holds the skill you want with a specific character. If said demon successfully dies at the hands of that character, you wil gain the option of adding that skill to your set. Later, certain game mechanics allow you to teach cracked skills to your demons.
 * The player's default weapon in Binary Domain is a an assault rifle. In early stages, it performs about as well as a standard assault rifle should against Mecha-Mooks. By the endgame, a fully upgraded assault rifle is practically a light machinegun tearing through hordes of mooks.