Victory-Guided Amnesia

"''This is not The Greatest Song in the World, no.

This is just a tribute.

Couldn't remember The Greatest Song in the World, no.

This is a tribute.''"

- Tenacious D, Tribute

You are one of the Big Damn Heroes. You've stormed the Evil Stronghold, rescued the Distressed Damsel, killed The Dragon, defeated the Big Bad, and even put the Sealed Evil in a Can they were worshiping in its place. Too bad you won't be aware enough of your own faculties to enjoy your victory. For some reason, one of the common rewards for a hero's victory is a one-way, all expenses paid trip to the Land of the Empty Mind, courtesy of Applied Phlebotinum Airlines.

Maybe the Powers That Be decided they became too powerful during their journey to remain as they are, or they discovered some Earth-shattering secret about life, the universe, and everything that needs to be kept under wraps, or maybe they did it to themselves, in an ill-fated attempt to just live a normal life or realize their dreams, but whatever the case, shortly after their final victory over the Forces of Darkness, they become amnesiac derelicts who can't even remember their own name.

... in extreme cases, that is. Most of the time, it's just a form of Brought Down to Normal that can also undo any Character Development. Now that's a reward for saving the world!

If Time Travel or Reality Warping is involved, victory may mean the past was rewritten so that the threat never existed, and neither did the struggles against it, even for the heroes.

Sometimes, to add insult to injury, whatever they did to stop those forces in the first place is only temporary, requiring them to regain their memories so they can put an end to it, once and for all. If the mind wipe was self-induced, Always Need What You Gave Up.

As with its supertrope, The Greatest Story Never Told, this is sometimes a component of a Bittersweet Ending.

Anime and Manga

 * A variant occurs in Fullmetal Alchemist:
 * In the 2003 anime version,
 * At the end of Pokémon the First Movie, Mewtwo erases all memories of him and the clones he created from the protagonists, to both protect himself from Team Rocket's boss and maintain some semblance of continuity.
 * Unfortunately the former doesn't take, as seen in Mewtwo Returns. At the end of that movie, he lets the protagonists keep their memories at their request . Later movies don't even try the latter.
 * Rave Master: Elie saves the whole universe from being destroyed in a massive explosion. Her second case of amnesia was induced by either  or using so much etherion.
 * Usagi does this in addition to a Reset Button at the end of the first season of Sailor Moon. This was the classic way to end a Magical Girl series; that the show was popular enough to undo this was actually quite subversive at the time. But then, Sailor Moon both made and broke Magical Girl tropes. Oh, and this doesn't happen in the manga, where the girls simply keep their memories.
 * Tekkaman Blade. After finally beating down the Radam forces (or at least ), D-Boy ends up getting amnesiac for real.
 * He had actually been amnesiac for a while before that - since right about the moment he set off for the Final Battle. He won the entire fight with Omega because the one thing that was left after his memory, personality, and even skills like speech were broken down was Unstoppable Rage.
 * Happens in Wedding Peach, which isn't surprising given how similar Wedding Peach is to Sailor Moon. The OVA series gives the girls their memories back, too; and, again, the manga doesn't do this.
 * That's rather misleading and wrong. Technically Wedding Peach for the most part averts this trope since unlike Sailor Moon it was not used in the TV series. It was actually created for the OVA series and then promptly retconned for the girls in the very same episode it was introduced.
 * in Weiss Kreuz Gluhen ends the series with a case of Victory Guided Amnesia following a Disney Death - arguably the best-case scenario, given the character's state throughout the series.
 * Pharaoh Atem in Yu-Gi-Oh! wiped his own memory and all existence of his very name from history after his initial defeat of Thief King Bakura and Zorc, only to have to scramble to regain both millennia later after both baddies return.
 * A borderline (And very depressing) case of this combined with A Fate Worse Than Death at the end of Zeta Gundam : After the defeat of Big Bad Paptimus Scirocco,
 * To Aru Majutsu no Index has a subverted example at the end of the series' very first arc. When Index goes Brainwashed and Crazy on her friends, she casts the spell "Dragon Breath" that causes feathers to fall from the sky. Coming into physical contact with just a single one is instantly fatal. When Touma undoes her brainwashing with his Imagine Breaker, he gets distracted by relief and one of the feathers graze his head. He survives due to Plot Armor but as a result of brain damage, all of his memories are destroyed permanently. He's fully aware of what happened but he can't undo it so he keeps it a secret and pretends nothing's wrong to keep his True Companions from worrying.
 * He's so good at it in fact that neither of his primary Love Interests figure it out until very late into the novels.

Comic Books

 * In a Retcon to explain the amnesia of Namor the Sub-Mariner in his first post-Golden Age reappearance, it was later said that in his final battle with the powerful psychic Destine, Namor was hypnotically commanded to fly as far as his little wings could take him, and simultaneously to forget his own identity. He wound up spending nearly a decade (or several, after the Sliding Time Scale got through with him) as an amnesiac derelict in the Bowery with a fear of water.
 * Marvel Comics' The Sentry - the world's greatest hero - saved the world from The Void, then makes everyone forget they ever heard of or met him, and he forgets he's a Superhero. It takes The Void returning for him to remember, and slowly others do too. Note that is entirely Retcon... The Sentry was created with this Backstory already in place.
 * It eventually turns out that
 * Occurs when  return from the Door At the Edge of the Universe in the first volume of Scott McCloud's Zot
 * Tintin and his friends didn't so much save the day in Flight 714 as save themselves from the bad guys, but either way their memories (as well as those of the bad guys) are wiped  at the end of the story, leaving only Snowy in the know.

Film

 * do this to the protagonists of Dude, Where's My Car? and all the innocent bystanders who watched them . This has the side effect of completely undoing all of their Character Development.
 * And then they send them gifts thanking them for doing what they don't remember doing, prompting yet another "How wasted were we last night?"
 * Christopher Nolan's Memento uses a version of this trope, but only because the main character suffers from short-term memory loss.
 * This happens to any Men in Black from Men in Black once they leave the service.
 * In the backstory of the movie Hook, Peter Pan got this after he left Neverland. Much of the plot hinges on him (now grown up) needing to relearn his basic heroic abilities (fighting and flying) in order to defeat a vengeful Captain Hook.

Literature

 * Used once or twice in the original Oz books by L. Frank Baum, where the heroes tricked the villains into drinking from a fountain containing the Water of Oblivion -- an amnesiac formula so powerful, it left the drinker still able to walk and talk...but not much else.
 * In Kristen Britain's The High Kings Tomb, the heroine saves the day by
 * Michael Crichton's Sphere. Doubles as a Shoot the Shaggy Dog.
 * The ending to Sphere is open to interpretation. I always thought . But it's hard to tell exactly what's going on because of the fact that the narrator gets/claims amnesia.
 * At the end of Susan Cooper's The Dark Is Rising series, the Lady chooses that John Rowlands forget everything that happened so he will not have to remember that . Merriman wipes the memories of the Drews and of Bran Davies.
 * In Will Eliot's The Pilo Family Circus, ex-clown protagonist Jamie uses some of his wishing powder to erase his memories of the circus. It doesn't work too well, as the Eldritch Abominations imprisoned below the circus - along with Jamie's boss, Gonko- keep trying to remind him of his experiences. And since he still has half a bag of wishing powder left, it's implied that he will one day use it to restore his lost memories, with catastrophic results.
 * In The Chronicles of Narnia, the four Pevensie children apparently entirely forget their lives outside of Narnia in the years that they rule (where do they think their parents are, then?). Then they're yanked back to our world. Susan apparently forces herself to believe it was all a fantasy after her last trip, to the point that she refuses the call to return in the last book.
 * In at least two of Andre Norton's novels (Android At Arms and The Crystal Gryphon) one protagonist wins the day by calling forth a powerful force that acts through them - but since they weren't in control at the time, they can't remember exactly what they did, or how. The latter had a sequel, in which the hero eventually learned to use power himself, without losing his own identity in the process.
 * In the fourth book of the Sword of Truth series, Temple of the Winds, Richard is only allowed to leave the temple by losing all the knowledge he gained from entering (which is to say, quite literally, everything there is to know about being a War Wizard; it's perhaps the only part of the series where he is in full control of his abilities). Perhaps an odd example, as he does remember the events that happened.
 * In Stephen King's IT, the children (except for ) begin to forget almost as soon as they beat IT and most of the as-adults portion of the novel is spent with them trying to remember. Once they beat IT the second time, their memories fade again (including  's) within weeks.
 * At the end of Brave Story,
 * In The Eternity Code, Artemis Fowl comes up with a scheme that will let him reclaim the stolen C Cube, but he requires fairy technology and the only thing he can offer in exchange is his own memories of them (which they long wanted to erase to maintain The Masquerade). Of course, being the Magnificent Bastard he is, Artemis finds a workaround...
 * In The Hounds of the Morrigan,
 * In Passage to Dawn, the 10th book of The Legend of Drizzt, Harkle Harpell uses a spell called "The Fog of Fate" to help the heroes solve a riddle. He ends up giving them too many hints, straining the limits of the spell, and as a result, is catapulted back home, having lost all memory of his participation in the quest.
 * In Devon Monk's Allie Beckstrom novel Magic to the Bone, Allie throws around a lot of magic at the climax. It has already been established that using magic can cause holes in her memory.

Live Action TV

 * Both the classic and the new series of Doctor Who have used this trope.
 * In the fourth season finale of the Doctor Who revival,
 * The classic series used this in "The Invasion of Time", where.
 * And at the end of The War Games too;
 * Happened to Daniel Jackson both times he returned from Ascending to a Higher Plane of Existence in Stargate SG-1. It was however subverted when he was de-ascended he was left with a certain degree of knowledge he had gained whilst ascended, and the potential to remember more of it (later becoming a major plot point).
 * The Star Trek: The Next Generation episode "Clues" deals with the crew realising they've lost an entire day, though they didn't really win or lose the "battle" fought during that day - they just reached a stalemate for which one of the requirements was a mind wipe. The first attempt failed because Data was immune; the second time, the crew agreed to it (and Data agreed to help cover it up), but they missed some details. The third time, they fixed those details and it finally worked.
 * Set up ahead of time in one episode of Dollhouse. Echo and several other Actives are given their original functional memories (without any declarative ones) and allowed to do as they please so that they can fulfill the desires that are causing trouble in brainwiping them later. As soon as they finish whatever it is they set out to do, they black out, leaving them ready to be put back in the chair.

Music

 * As quoted above, the Tenacious D song "Tribute" is a tribute to the "greatest song in the world" that Jack and K.G. performed to defend themselves from the Devil. However, after this event, the actual song fades from memory, but they know it wasn't anything like "Tribute" itself.

Tabletop Games

 * When a Promethean reaches the New Dawn, they make a roll that basically determines whether they've been acting more human than Promethean (bonuses for fulfilling Vice or Virtue, penalties for using Transmutations). If they succeed, they've been leaning towards human and remember everything; if they fail, however, they've been leaning towards Promethean, and everything pertaining to the Pilgrimage is boiled away. Leaving them with a strong case of amnesia and likely no record of existence... but the universe no longer hates them.

Video Games

 * Castlevania: Julius Belmont promptly became amnesiac after he defeated Dracula and sealed him up "for good" in 1999. It took a tour through Dracula's castle 35 years later for him to regain his senses.
 * Time Travel is a common cause of this. Just ask the protagonists of Final Fantasy I! Oh wait, they don't remember...
 * Except they do if you're playing the GBA release; according to the scrolling text at the end, they're the ONLY ones that remember what happened.
 * The NES version, on the other hand, makes it clear that the only person that will remember their victory is the player.
 * In Metal Gear Solid Mobile, Philanthropy's first mission is revealed to be a VR simulation, with a kidnapped Snake locked into the sim and taking orders from an artificial Otacon, while the real Otacon was on the sidelines, attempting to hack Snake's brain out. Eventually, he was forced to complete the simulation to get out, but, as he failed to provide the data his captors needed, his mind was wiped of the event and he was returned to Otacon. Gets especially glaring when you realise Otacon would still remember. Gets even more glaring when you realise it wouldn't even cause a real continuity problem if Snake remembered the events and would even help justify his seemingly irrational distate for VR in Metal Gear Solid 2.
 * Near the end of Overlord you discover that lost his memory after being left for dead.
 * Occasionally happens in the Persona games. A major problem arises when one of the crew of Innocent Sin doesn't forget in Persona 2: Eternal Punishment. The good ending of Persona 3 has the True Companions remembering regardless of reality trying to prevent that, arriving just in time to see.
 * The bad ending of Shadow Hearts 2 has.
 * After saving the world in Soul Blazer, the Blazer (who was created by God to save the world) has returned to heaven as his work is done. A year later he misses life as a human and the girl he had met early along the way.
 * This is the ending of Chrono Cross if you end the final boss battle correctly. Kill the Giant Space Flea From Nowhere, save the multiverse, ...
 * You pass one of these in Baldur's Gate 2. In the Spellhold asylum, one of the inmates is a former bard of repute who, in his search for the answers of the universe, is mentioned to have gotten too close to something that didn't like him poking around. You have no way of knowing what really happened, but his mental faculties are now at the level of maybe a 5-year-old, he talks about little except his "many many pretties, piled high beyond the skies" and has an infinite and inexplicable supply of precious gems.
 * All over the place in Kingdom Hearts.
 * At the beginning of Chain of Memories, Sora loses all recollection of the events of the first game. At the end,
 * Done twice in 358/2 Days, where
 * Also at the end of Birth by Sleep, where
 * And in the secret movie "Blank Points," where it's revealed that
 * And once more in Coded, where
 * Both the supposed Big Bad and supposed Big Good of Arcanum, due to voluntary or involuntary isolation, are shadows of their legendary power.
 * Implied in Final Fantasy VII, albeit in a very screwy way: Zack manages to achieve victory (protecting Cloud from Shinra), but Cloud is the one who ends up with amnesia.

Western Animation

 * Futurama, "The Why of Fry": Nibbler wipes Fry's memories after he saves the universe from the brainspawn.
 * This is repeated several more times to the point of parody; Bender's Game shows the characters unfazed by Nibbler's speech because he forgot to erase their memories last time.
 * Also, everyone on Earth (except Fry) forgot about the Brainspawn after Fry foils their invasion.
 * At the end of It's Your First Kiss, Charlie Brown, Charlie Brown doesn't remember that he worked up the nerve to kiss the Little Red-Haired Girl at the Homecoming dance and subsequently was the life of the party. (It's probably for the best that he also forgot "losing" the football game beforehand - the viewers would sure like to forget that one.)
 * At the end of the Kim Possible movie "A Sitch In Time", none of the characters remember saving the future from being taken over by Shego thanks to Ron breaking the time traveling monkey that caused the whole mess to begin with.
 * Transformers Prime, after Optimus Prime