Situational Sword

A sword, or any other type of weapon, that unleashes some form of "hidden" (or not so hidden) power when certain conditions are met, such as the wielder nearing death, blood getting splashed on it, etc. This weapon tends to be most prominently used in a Desperation Attack.

Situational Swords are similar in concept to the Empathic Weapon, but generally tend to be non-Sentient. When an Empathic Weapon is a Situational Sword, it is usually Loyal Phlebotinum. Compare Evolving Weapon for weapons that "level up" and Full Potential Upgrade for weapons (and tools) that have to be powered-up along with the character.

A common subtrope is Weapon of X-Slaying.

Anime and Manga

 * One story of the Crying Freeman anime OVAs involved several parties falling under the curse of the Muramasa blades (explained below), which made the user go berserk until the sword left their grip.
 * The Medicine Seller's sword in Mononoke can only be drawn when he learns more about the titular monsters. But once he gets the Shape, Truth, and Reason, asskicking ensues.
 * Rave Master uses the Ten Commandments sword, which has a total of 10 separate situational swords. However, Runesave is the one that stands out the most, simply because it only cuts things that couldn't be cut, like the wind or magic.
 * In Inuyasha, the titular half-demon was given a sword by his father that becomes much more powerful if he's trying to protect a human from a demon.
 * An even better example would be his brother's sword, a Healing Shiv that's useless against living beings but happens to be the only weapon that can cut spirits or other enemies that are Made of Air.
 * Ranma ½'s Cologne owns the Poison-Cleaving Sword, a semi-sentient Chinese dao with a flower at the tip. This flower has a mouth, and it detects poison and warns the wielder when poison is nearby... and then tries to run away from it, pulling the wielder along if necessary. The reason? Although the Poison Cleaver can indeed cut through any poison and render it harmless, it dies after just one stroke. And, in its own Hamlet's words, the rest... is silence.
 * Kaito from Hunter X Hunter wields the... well, weapon Crazy Slot which randomly takes the form of one of nine weapons when materialized. These include a rifle, a Sinister Scythe and a club. He cannot dematerialize or switch it until used.
 * In Katekyo Hitman Reborn, Yamamoto has two weapons like this: A baseball bat that turns into a sword when swung at a certain (fast) speed, and a bamboo sword that turns into a real one when he uses his special techniques.
 * Naruto presents us with the Seven Swordsmen of the Mist, each of which posses a sword with a special ability. Starting off, Kisame Hoshigaki has a shark themed sword that can eat other people's chakra, among other things. The most interesting, though is that after all these years, we finally find out that the sword of Zabuza Momochi, the first Swordsman ever met in the series and original Big Bad before his spectacular Heel Face Turn, actually does something other than look menacing and heavy. It can repair itself by sucking the iron out of someone's blood.

Comic Books

 * The titular heroine in Empowered has a suit that makes her a not-entirely formidable crime-fighter, but once, when she was saving her best friend's life, it grew a pair of glowing wings and unleashed awesome power. She still doesn't know exactly what stimulus caused it (though it's a safe bet it was emotional).

Film

 * In District 9 Prawn guns and tech are created organically and do not work when used by humans. The prawns are either too passive, too wild, or too undesirable to be used in human armies. Thus, MNU has spent the considerable part of three decades trying to develop test subjects with combined working prawn/human DNA so that they can develop a Super Soldier program.

Gamebooks

 * Lone Wolf: The Sommerswerd's "supernatural powers increase the bearer's CS by 8 (prior to the application of weapon skill bonuses), and also increase the sensitivity of his Sixth Sense. It is doubly damaging to undead foes and absorbs hostile magic. Perhaps its greatest power is the ability to kill Darklords, and it's possible, as stated in The Curse of Naar, that it might be able to kill Naar himself. Only members of the royal house of Sommerlund or a Kai Lord can wield it. If anyone else uses it in battle, it will slowly and irrevocably lose its powers." On the other hand, whip it out in the wrong spot, every Tom, Dick and Rubicante shows up to kick your ass.
 * Fortunately, evil beings can't take advantage of this to depower the sword—if you happen to be evil and try to hold the sword it will melt your fingers off.

Literature

 * Tortall Universe: Alanna's sword Lightning reveals its powers only after she has
 * In James Swallow's Warhammer 40,000 Deus Sanguinius, Rafen learns that to wield the Spear of Telesto, he must
 * Felix's sword in Gotrek and Felix is enchanted to kill dragons and will grant its wielder extra strength and other bonuses, but only when fighting a dragon (or to get him through a fight so he can go fight a dragon later).
 * In P.C. Hodgell's Chronicles of the Kencyrath series, the hereditary sword of the house of Knorth, Kin-slayer, can cut through opponents as if they were butter—but only when wielded by someone wearing the Knorth signet ring on their finger. Furthermore, it cannot be sheathed until it has killed someone, and the energy of the sword numbs the hand of the bearer. Meanwhile, the Ivory Knife, an ancient heirloom artifact reputed to come from the Kencyrs' God, kills from the merest scratch. It is called "the very tooth of Death."
 * The sword Sting from Lord of the Rings glows blue when orcs are near, and is an effective weapon against them. It's also effective against Giant Spiders such as the infamous Shelob. In fact, Sting got its name after Bilbo used it to rescue his dwarf companions from a horde of lesser Giant Spiders
 * The dagger Merry attacks the Witch-King with was also specifically made to fight beings of his nature, and so does crippling damage despite the Witch-King being a Ringwraith. In other situations, it's merely a decent hobbit-sized sword.
 * Parodied in Terry Pratchett's The Wee Free Men: the Nac mac Feegle have swords that glow blue in the presence of lawyers.
 * Some of the Swords of Power from Fred Saberhagen's Book of Swords series have situational powers.
 * Shieldbreaker makes the wielder nigh-unbeatable in battle, but only if he's fighting an armed opponent.
 * Townsaver has similar powers, but only functions when defending an inhabited place
 * Dragonslicer is the epitome, it only has magical powers when wielded against a dragon.
 * Stonecutter too. It's only "magical" property is the ability to cut through stone.
 * The titular weapon in Lawrence Watt-Evans's Ethshar novel The Misenchanted Sword will do your fighting for you, but only against adult male humans, and once it kills, you have to sheath it and draw it again to re-activate its power. Also, you can't resheath it, or even let go of it, until it's killed someone.
 * Also, no one else can use it, and you will die if and only if you have killed a hundred men with it (at which point it turns on you and finds a new owner - they will then remain alive until their 99th kill, and so on until some poor soul is slain on first drawing the blade). At first the character is unnerved by not knowing how close he was and that he could die at any time. Later, the character realizes it was Age Without Youth and desperately tries to find a way to kill the last men.
 * Among its many other properties, the sword named Need in Mercedes Lackey's Heralds of Valdemar series provides a considerable amount of protection from magic if it's wielded by a trained fighter. If wielded by a Squishy Wizard, on the other hand, it gives no magical protection but instead makes the mage an expert swordswoman. In the hands of someone with no particular talents in either direction, it does both (and some other neat tricks besides). Regardless, it only functions for women.   What might have happened if Need were wielded by a genuine Magic Knight is never quite shown in the series, since by the time it's an option, Need.
 * In The Neverending Story, Bastian receives the magical sword Sikanda. The sword is amazing, and quite possibly alive, evidenced by the way it guides Bastian's hand and makes peerless, flawless cuts once it leaps out of the sheath, but there are a number of limitations. First of all, only those who have eaten, drunk, and bathed in the flames of the Many-Colored Death, and ridden on his back, may touch the sword without danger (Bastian has to disappoint a few good men who wish to be knighted by the blade because of it). Secondly, Bastian may only draw the sword and use it when it leaps willingly from the sheath. At the height of his growing madness later in the story, Bastian attempts to use Sikanda to fight . The sword refuses to budge from the sheath, but Bastian continues to tug at it, and finally tears it out of its sheath by brute force. In that instant, a terrible sound echoes through the tower, and Sikanda's light is lost forever.
 * The black sword Dyrnwyn from the Chronicles of Prydain series can only be drawn by one of "noble worth". Taran at first assumes this means one born of a noble bloodline, but Gwydion later states that it is referring to character, not blood. In the hands of a worthy person it is an Infinity+1 Sword capable of slaying just about any evil being. Those who are unworthy tend to get themselves killed trying to draw the sword. Taran has to go through four or five books' worth of Character Development before he can wield it.
 * In Blue Moon Rising by Simon Green, the hero finds a sword which, if its wielder is in a desperate situation and his concern is less for himself than for others, will call down a magical rainbow that disintegrates the supernatural evils caused by the Blue Moon. He nearly gets killed trying to invoke the rainbow in a tight spot where he's the only one he's really worried about.
 * Percy Jackson's sword Anaklusmos (Riptide) is made from celestial bronze, and is only effective against monsters or those with divine blood such as other demigods. It is completely harmless if used against regular humans.

Music

 * The titular blade from "The Arizona Sword" by Leslie Fish appears to have been enchanted to turn on its wielder if he tries to use it for unjust reasons.

Mythology

 * Tyrfing from Norse mythology was under a similar Curse for a long while. If drawn, it must take a life before it can be put away.
 * This included one occasion where its wielder, an Action Girl, had to kill a guy who just took it out of the sheath to look at it. There was no punishment for this, probably because she'd explained the curse beforehand and thus everyone present wrote the guy off as Too Dumb to Live.

Tabletop Games

 * The rules for intelligent weapons in D&D include the option of a special purpose that comes with a matching special power only used in the pursuit of said purpose. The chance for a randomly rolled magic weapon to have this property is somewhere around 1% or less.
 * You don't have to go quite that far, however. Unintelligent weapons with situational bonuses and/or powers are likewise a long-standing and rather more common D&D staple. Sword + 1, + 3 vs. spellcasters, anybody?
 * Weapons of Legacy. There's no plot device or game mechanic someone didn't try to stick in D&D, so they made an entire D&D 3.5 sourcebook dedicated to weapons with specific purpose that unlock abilities via "achievements"/quests.

Video Games
"[Name of character] lets out a howl. Critical hit.
 * Link's sword in The Legend of Zelda shoots energy beams when he's at full health in the 2D games, otherwise it's limited to melee.
 * The Master Sword is also known as the Sword of Evil's Bane, and can reflect evil magics. It's also stated to be unweildable by anybody but the true hero, and untouchable by evil, but those never play much of a part in the actual games. It also serves as a lock at least twice. In Ocarina of Time it hides the Triforce from evil, and in Wind Waker
 * At least until his next incarnation.
 * Seen a lot in Final Fantasy games, notably with weapons like Ultima Weapon (attack strength is tied to HP,) the ancient sword (chance of putting enemies to sleep,) and some weapons in Final Fantasy VI (which unleash spells when used on occasion.)
 * Final Fantasy III and IV both allow you to cast spells from weapons if you select said armament from the inventory.
 * As did the original game - some weapons would randomly cast spells when hitting a monster, others could be used as items to cast a spell (like Heal or Lightning) even by non-spell-casting characters. Leading to wonderful benefits like being able to cast Lit2 on sea monsters as a White Wizard using Thor's Hammer.
 * Final Fantasy V has a job class devoted to making swords Situational, the Mystic Knight/Sorcerer.
 * All the Ultimate Weapons in Final Fantasy VII have effects like this, with some examples being the aforementioned Ultima Weapon, Vincent's Death Penalty (does more damage dependent on how many enemies he's slain), and Tifa's Premium Heart, which does damage based on how much of her Limit gauge is full.
 * Final Fantasy XI has many weapons (and armor!) that will be stronger or have added effects depending on anything from the time of day, to the moon phase, to the weather, to whether or not you have a specific Standard Status Effect on you, etc.
 * Castlevania: Symphony Of The Night has swords such as the badelaire, which powers up as the in-game clock counter increases, and the muramasa, which gets stronger if you strike enemies capable of bleeding.
 * Most of the weapons in Order of Ecclesia are based around the idea of being used in conjunction with each other, i.e. if you use two wind glphys and throw them simultaneously, they will create a screen-high tornado.
 * In Golden Sun the special named weapons will randomly unleash a special attack instead of a normal critical hit. This changes the dialogue from;
 * to

[Name of weapon] lets out a howl. [Name of special effect/attack]"


 * Baldur's Gate has one kind of sword that glows when enemies are nearby, though unfortunately it counts normal-sized rats and spiders as enemies even though they can't hurt you. Also, weapons 'Of Disruption' have a chance of instantly vaporizing undead upon contact. The oringinal also had a nifty 'Greatsword +1/+3 vs. shapeshifters' (which you fough a lot of).
 * Carsomyr also has a bunch of abilities which while technically always active only really come into play when facing spellcasters.
 * Dragon Age also has plenty of these. In fact, using runes the player can opt to make their weapon like this ie. +10 damage to darkspawn.
 * The Dark Cloud series has the Lamb's Sword. In the first game, allowing the Lamb's Sword to reach critical WHP transforms it into the much stronger Wolf Sword until it is repaired. In the second game, the sword becomes the Wolf Sword from 9PM until 6AM, again with a boost in attack power.
 * In 3D Dot Game Heroes, weapons are effectively useless unless you are at full health, at which point the upgrade abilities that either came with the weapons or were bought later kick in.
 * Chrono Trigger: Robo's ultimate weapon, the Crisis Arm, has its power depend on Robo's last digit of HP. If the last digit is 0, it does no damage. If the last digit is 9, then it can consistently outdamage everyone except a level 99 Ayla. Thankfully, Robo hits 999 HP relatively early, so keeping the Crisis Arm powerful is merely a matter of keeping Robo as close to full HP as possible.
 * The DS remake gives Lucca the Spellslinger, a similar weapon based off the last digit of her MP.
 * Several weapons in Team Fortress 2, including the Axtinguisher which does critical (triple) damage to burning players, and the Equalizer which does more damage and makes you run faster if you are low on health.
 * And the Sniper's Bushwhacka which does critical damage whenever it would normally do a mini-crit, usually against a victim of Jarate.
 * In the Sonny series of flash games, many of the techs for the Shadow Psychological build are situational to the point of being frustratingly inconvienient at times, causing many to prefer the Electric Psycho build. In the Cold Hydro build, there is one attack called Shatter that can only be used on opponents who have 3 Ice elemental debuffs (if one debuff expires before Shatter can be cast, then it won't work).

Web Comics
"Zoe (Face Palm): I want the blood of the innocent to rain down in every room of our house. Later-- Gwynn (cleaning): Did you have to say every room?? Zoe: I couldn't remember which room it was in!"
 * Almost every named character that fights in Goblins has a weapon that works like this: Big Ears' axe, Complains' magic shield that does a random (usually offensive) countermove every time it is struck, Dies-Horribly has a psychic artificial arm, Chief's spear does a Macross Missile Massacre if he throws it, etc.
 * Tavor's swords in Looking for Group reveal a map to Kethenecia when coated in blood.
 * Torg has a magical sword (dubbed Chaz) that, upon "drinking" the blood of an innocent, can cut through anything and speak. Torg is typically too nice of a guy to actively acquire the needed blood. The most amusing case was when his friend Zoe, unaware of Chaz's true nature and utterly stupefied by the suggestion, made her single wish to a demon. Afterward, Torg used the now-awakened spirit sword to kill it.


 * Since being reforged with starmetal, Roy's sword in Order of the Stick occassionally channels energy that is harmful to undead and evil outsiders.
 * In a parody of the Lord of the Rings example, Lambert of Irregular Webcomic has a magic sword that sings "Don't Stand So Close to Me" when orcs are near

Web Original
"Church: So, it is a sword. It just happens to function like a key in very specific situations. Caboose: Or... it's a key all the time... and when you stick it in people, it unlocks their death."
 * In Red vs. Blue, Tucker's energy sword can function as a key at times, but is otherwise still a powerful weapon.

Western Animation

 * He-Man and the Masters of the Universe and She Ra Princess of Power give us the Sword of Power and the Sword of Protection, respectively. In a jam? Stab the Sky and invoke the Power (or Honor) of Grayskull. Super-Powered Alter Ego invoked, problem solved.
 * Samurai Jack's sword will not cut anyone pure of heart, as evident both when Aku stole it and tried to stab Jack with it and when Jack tried to use it to cut up a deer for food.
 * The sword Rubilax in Wakfu is technically a four-element demon, and therefore assumably has as many forms in addition to his normal one.
 * Lion-O of Thundercats fame possessed the Sword of Omens, a nifty sword that in addition to its "Sight Beyond Sight" ability and its power to call upon the other Thundercats, could literally get him out of any situation. For example, on one occasion it essentially transformed into a vaulting pole and propelled him up the side of a castle.

Real Life

 * Smart guns are prototype firearms that use a unique locking system to prevent anyone who doesn't have the matching magnetic key from firing them.
 * There are a number of systems: RFID tags, grip patterns, fingerprints.