Unholy Holy Sword

The MacGuffin and Applied Phlebotinum's reply to The Mole.

In many stories with fantastical or sci-fi elements, there's one particular object or weapon that the heroes rely on--perhaps a Cool Sword or Orphan's Plot Trinket that just so happens to be the source of their powers. It will always be stated as innocent or innocuous at the least, and outright holy at the most extreme. In both cases, this is the hero's trademark weapon and the crutch by which they battle and carry out their adventures; if it's of the sacred variety, the heroes may use it as a crutch for the morality of their actions, too: Sure, it might leave a bad taste in their mouths to have killed the sympathetic Anti-Villain or the Tragic Monster, but they have their holy sword! They must have the forces of Good behind them, so it's all right!

Of course, in a case like this it's not that pretty--this weapon or object just happens to work through evil means. Perhaps it's simply Powered by a Forsaken Child, or perhaps it happens to be a keystone in the villain's plans, and he's manipulating the heroes into handing it over to him or even powering it up for him.

The Reveal of this information is expected to be proportionately dramatic to the item in question's plot importance. Depending on what point in the plot the truth comes out, a variety of outcomes can occur:


 * If the truth comes out early in the plot, viewers can expect a brief Heroic BSOD or Ten-Minute Retirement in which the heroes attempt to cast aside the Unholy Holy Sword in disgust. Sometimes they can find another power source, although usually they are persuaded to keep using it until the world is saved, when they can stop using it safely.
 * Alternately, the hero may attempt to purify the Unholy Holy Sword so that it really can be used safely and in the name of good. (This doesn't really work with Powered by a Forsaken Child examples, though (unless you can find a different power source - maybe one that works even better!).)
 * If the Unholy Holy Sword is very plot-important or The Reveal occurs during the climax or penultimate stage of the story, the plot may very well shift in the direction of sealing or destroying it so that no one can use it again, if not a full-on dramatic confrontation with the villain over its true purpose.

Not to be confused with Sealed Evil in a Can, where the object contains something evil; this MacGuffin is innately bad. Related to the Amulet of Dependency, the Evil Weapon, and the Artifact of Doom, where an item like this is Obviously Evil.

Needless to say, this is a SPOILER trope, so if you happen to be spoiler-sensitive, avert thine eyes.

Anime

 * The Shikon no Tama of Inuyasha: its powers come from the fact that a very powerful demon and an equally powerful Miko are sealed inside of it and battling fiercely. It is finally revealed that the demon soul inside of the Shikon Jewel is a Man Behind the Man to Naraku, hoping to switch places with him and be free again.
 * The Sword of Light in Slayers was originally thought to be a weapon of good, passed down in Gourry Gabriev's family. It was originally used to defeat the Demon Beast Zanaffar, and was seen as an object of great good for a long time by the entire world. Then, in Slayers TRY, it was revealed to be part of a set of five similar weapons from another dimension, which are that reality's version of the Five Dark Lords.
 * In Night Wizard, the seven Jewels of Virtue the heroes are collecting turn out to be fragments of (God of Destruction) Shaimal's power. Once the Jewels are brought together, Shaimal begins to awaken within Eris, who's horrified upon learning that she's just a vessel for Shaimal's reincarnation.
 * In Claymore, the titular Claymores are girls who have the flesh of Yoma (human-eating monsters) implanted in their bodies to give them inhuman strength, speed, and other powers.

Comics

 * The amulet in Amulet. Use it too much, and it does very bad things to you.
 * The Red and Orange Power Rings in DC Comics (specifically the Green Lantern books). Not only are they powered by rage and greed, respectively, but their wearers become consumed with those emotions as well. Yellow Power Rings are fear-based, but their wearers generally retain their personalities.
 * The Violet Power Rings are powered by love and cause their wielders to become obsessed with it, though not to the extremes of the original Star Sapphires. OTOH, this is partially due to the brainwashing most recruits go through before they are taken into the Corps.

Live-action Television

 * In Buffy the Vampire Slayer it turns out the power of the Slayer line began when the First Slayer was imbued with the power of a demon.

Film

 * In the movie Feng Shui the lead character receives a "lucky" ba gua mirror. It is in fact lucky, in the superficial sense, but it also turns out everyone who looks in the mirror dies according to their Chinese zodiac sign.

Literature

 * In the Inheritance Cycle, the sword Eragon gets from Brom, Zar'roc, is later found out to have belonged to the last of the Forsworn, Morzan, who was killed by Brom.
 * Over the course of The Hobbit and Lord of the Rings, the One Ring is treated something like this--it's Bilbo's most prized artifact and gets him out of a lot of trouble, but once its true nature is exposed, it takes a narrative six times longer than the first book to destroy it safely.
 * Gurthang, the sword of Túrin Turambar in J.R.R.Tolkien's The Silmarillion. It enables him to slay dragon Glaurung, but it also claims the lives of many of his friends and loved ones, and in the end his own. (It's a very hungry sword and it will drink the blood of anyone, including its wielder.)
 * In Memory, Sorrow, and Thorn, the swords they believe they need to gather to stop the Storm King are actually the key to his return. This becomes the third version, as, after the reveal, the focus of the story abruptly shifts to how to stop the badguys from using them. Of course, You Are Too Late, forcing the heroes to Take a Third Option.
 * In The Night Angel Trilogy, the ka'kari, particulaly the black, act as this. While not evil, the ka'kari is central to most of the villains plans, as it grants immortality via stealing the life energy off the bonded person's loved ones everytime the user dies. Needless to say, when Kylar learned of it, it was already bonded with him and he had died 5 times already.
 * In The Secret Histories novel The Man with the Golden Torc by Simon R. Green, it's revealed that the golden armor that the Drood family wears, that makes the super powered and indestructable, are powered by the souls of their dead twins which are consumed by The Heart (a giant, living crystal with godlike powers) shortly after birth.
 * This is undermined at the end of the book with the destruction of The Heart at the end of the book by another trans-dimentional being called Strange Matter that gives them armor with the same powers that are not fueled by dead babies.
 * In The Secrets of the Immortal Nicholas Flamel, the elemental swords are well known- one is Excalibur. They also all actively consume the memories of those wounded by them, and eventually the minds of an unprotected wielder, and can potentially destroy the world if united. The heroes use one. Oops.
 * The Subtle Knife from Phillip Pullman's trilogy, His Dark Materials. The knife can cut through dimensional barriers and enables the majority of the plot to happen. However, not only are the holes it creates.
 * Stormbringer is a decided aversion, though it probably needs to be mentioned because it keeps popping up on this page anyway. While the sword does provide Elric with much of his strength and proves as effective when used against the forces of Chaos as against most other things, nobody even passingly familiar with the weapon is fooled in the slightest into thinking that it is not evil.

Video Games

 * Yggdra Union has the Gran Centurio, which just so happens to be the Trope Namer. For centuries, it was believed to be a symbol of justice incarnate. However, it was eventually revealed to be a power generator that a manipulative fallen angel planned to use as the instrument of his revenge against the gods. It so happened to run on people's hatred and pain.
 * The Gran Centurio also plays a small role in certain paths of Blaze Union and Yggdra Unison.
 * Along with its Captain Ersatz from Rondo of Swords, though that game took the second approach.
 * Exspheres in Tales of Symphonia. Although The Reveal happens early, Exspheres and the ramifications of using them continue to feature in the plot even after the heroes are persuaded to keep using them for now.
 * Also blastia in Tales of Vesperia.
 * Soul Calibur of the Soul Series turns out to be as bad as the sword it's designed to counter. Soul Edge itself is an example, too.
 * The backstory of several Korean characters involves their trying to find the "Sword of Salvation" in order to drive out the Japanese. At first they thought it might be Soul Edge, the mcguffin pretty much everyone else is after. After seeing its evil true nature in Soul Calibur II they spend the rest of the series warning people of its manipulative nature, and trying to destroy it with Soul Calibur. Then Talim makes them realize Soul Calibur is just as bad.
 * Sudeki; the first half of the plot revolves around collecting crystals to power a "Peace Shield" around the kingdom of Haskillia, protecting it for all time. As it turns out, the crystal actually gain their power by sucking the "light" (akin to Life Force) from the mirror dimension of Akloria, leaving it to essentially rot as Haskillia blooms. To say nothing of the machine's real purpose, summoning Heigou...
 * The Seru in Legend of Legaia might be borderline in the backstory, seeing as they're living armor and weapons that symbiotically bond to their human wielders... and have an unfortunate propensity for getting Brainwashed and Crazy and taking those wielders with them. The entire plot of the first game involves the heroes trying to fix a world terrorized by insane Seru.
 * Frostmourne in WarCraft III. It was originally the sword of Ner'zhul (the Lich King) which he trick Prince Arthas to use (which he did believing it was the only way he could defeat the plague of the undead) while its true purpose was to corrupt Arthas into joining him.
 * The Ashbringer zig-zags around this trope. The crystal that it was made of started as evil, but was purified. The sword itself was created as good, later corrupted, and then purified again. And then there are theories that the crystal is somehow related to Naaru, or is one, going through their dark/light reincarnations.
 * Quel'Delar, the Infinity-1 Sword of World of Warcraft: Wrath of the Lich King, goes through this stage briefly during the quest to reforge it. When it's been reforged with saronite, an ore that is actually the blood of a major Eldritch Abomination (Made of Evil, of course), it draws its owner to the vicinity of Frostmourne and attacks on its own accord. After that, it too needs to be purified.
 * The Grandlion/Masamune in Chrono Trigger is a complicated example. It's first mentioned as a heroic knight's blade, but turns out to have been filled with the power of Lavos, but is also powered by a pair of playful spirits that react to people's dreams. So it goes from good, to bad, to neutral, to good again. By Chrono Cross, it's been tainted again (by a powerful person wielding it for evil), but you can fix it.
 * Chrono Cross also has the Records of Fate, which are revered in Arni as if they speak some divine and benevolent will, but it turns out they're used to control the islanders by a computer aptly-named FATE.
 * Brave Fencer Musashi features Lumina, the sword of luminescence, which was used to defeat the Wizard of Darkness in the distant past. Musashi claims it early in the game, and spends most of the rest of it finding and claiming the Five Scrolls that increase its power. Naturally, upon acquiring the final one, it turns out that Lumina wasn't just used to defeat the Wizard of Darkness, the Wizard of Darkness was sealed inside of it and the scrolls have been breaking the seal.
 * Arcadion the Shade Sword, or The Black Sword, from Ultima VII: The Black Gate (the Forge of Virtue expansion). Forged from a supernatural metal and empowered by its captive demon, it is a superb weapon that can kill anything that capable of dying, possesses many other potent powers, and the demon can offer plenty of advice on matters. On the other hand, it is a demon-powered sword and you're supposed to be the Avatar, a champion of Virtue. It's fairly far-fetched for you to want to wield the thing, or forge the cursed thing in the first place. You can avoid it by not completing the expansion, but since you start with it in Serpent Isle, Arcadion is canon.
 * Heroes of Might and Magic 4 has the Angel's Blade. It's not necessarily evil, and it's primary function is killing undead and demons, but a quest during the campaign reveals it was created by a demon. It doesn't really matter since 1) the main character is a necromancer fighting other demons, and 2) he only needs the sword because the energy released when destroying it, will open a portal to where he needs to go.
 * The last campaign of Heroes Chronicles revolves around the Sword of Frost, an extremely powerful sword which is being sought by the Barbarian King Kilgor as a counter to Gelu's Armageddon's Blade, by Gelu to destroy Armageddon's Blade and keep the Sword of Frost out of Kilgor's hands, and by Tarnum to both keep it out of Kilgor's hands and keep Gelu from destroying Armageddon's Blade in the wrong way. Sadly, the wrong way that the Sword of Frost ends the terror of Armageddon's Blade is what happens... and it is by blowing up the world, leading to the events of HOMM 4.
 * The Elder Scrolls IV Oblivion has a variation, where there is a sword that is holy (wielded by a powerful time travelling berserkser-saint who was a robotic xenophobic personification of a missing god, no less) that was cursed afterwards by someone who used it in a war for material conquest.
 * The Neverland games by Idea Factory invert this repeatedly with a whole slew of weapons with more or less ominous names that turn out to be potent forces of good. Among others, Demon Princess Hiro's Gate of Hell scythe can sunder someone's soul from their body and send it straight to Hell, but only works on those with an extremely evil spirit, and the Evil Spear Aleph-Beth was the weapon of choice of Arth, a holy angel who ascended to godhood and, in spite of his sudden fit of rage against humans at one point in history, was actually one of the few ascended gods who WEREN'T homicidal maniacs.
 * Kite's Bracelet from the .hack R1 games
 * The Monado in Xenoblade Chronicles. It's valued by the Homs for being one of the few things able to harm the dreaded Mechon, and is used by Shulk to save the lives of his friends numerous times, thanks to its abilities to let him see the future and effectively warp reality to some degree.

Visual Novels

 * The aptly-named Sword from the yuri VN Aoi Shiro. It was used to summon divine storm that sunk the invading Mongol fleet in the past. Partially subverted, those with qualifications to use it know that it's holy in the sense that "this item with terrible power is a property of the gods, do not touch", not "this is a weapon to battle evils". Also, it's not mentioned as such during the game itself, but it's the Kusanagi. It was originated from the Chaos that people in the past called Orochi, and will definitely, without exception, corrupts its user.
 * The wish-granting Holy Grail in Fate Stay Night literally holds all the evil in the world, and can only grant wishes through destruction. However, this is because the summoning of an eighth Servant, Angra Mainyu (Avenger), during the Third Grail War inadvertently tainted the Grail - it wasn't like that to begin with.
 * In the third route of the Visual Novel, there's also Saber's Excalibur. For the first 2 routes, it is a holy "Sword of Promised Victory" that fires off a beam of bright light. Halfway through the third route she is corrupted by the evil in the Grail . The switch from Lawful Good to Lawful Evil is accompanied by her sword turning into the pitch-black "Excalibur Morgan" and firing off red/black beams. This is explained as being due to Morgan Le Fay's hand in it's creation.

Webcomics

 * Inverted in Goblins by the Axe of Prissan. It was designed to generate an aura of evilness, so that any paladins who are aware of it would seek it out in order to destroy it. Once they discover the axe, it telepathically communicates to them that its actually being used to imprison a powerful demon who once tried to invade the Prime Material Plane, and that a paladin must constantly use it to do good deeds, which will strengthen the wards of the demon's prison.