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** Goku turning into a child is part of the whole ''concept'' of ''Anime/DragonBallGT''.
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** In ''Anime/DragonBallGT'', Emperor Pilaf has gathered the [[ArtifactOfDoom Black Star Dragon Balls]], only for Goku turning into to show up and easily defeat his minions. Enraged, Pilaf screams that he wishes Goku was a child is part again so that he'd be easier to defeat, which Shenron grants. Goku remains in this state (except when transformed into Super Saiyan 4) for the rest of the whole ''concept'' of ''Anime/DragonBallGT''.series, only returning to adulthood in [[spoiler:the DistantFinale]].
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** From the twelfth movie ''Anime/OnePieceFilmZ'', Ain's Modo Modo no Mi powers allow her to rejuvenate her opponents. Unlike Bonney's powers, however, it works on inanimate objects too, and it can only work backwards, whereas Bonney can also age her opponents. [[spoiler:Nami, Chopper, Robin, and Brook all got hit by it, regressing the former two into children, Robin into a teenager, and... not altering Brook's physical appearance at all, [[DemBones since he's a skeleton]].]]
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** From the twelfth movie ''Anime/OnePieceFilmZ'', Ain's Modo Modo no Mi powers allow her to rejuvenate her opponents. Unlike Bonney's powers, however, however, it works on inanimate objects too, and it can only work backwards, whereas Bonney can also age her opponents.opponents (the trade-off is that Ain can inflict DeathByDeaging, while Bonney's powers are only temporary when used on living targets). [[spoiler:Nami, Chopper, Robin, and Brook all got hit by it, regressing the former two into children, Robin into a teenager, and... not altering Brook's physical appearance at all, [[DemBones since he's a skeleton]].]]
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Added the most recent The 100 Girlfriends example.
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** Chapter 167 is another invoked repeat, with the girlfriends from Ahko to Matsuri becoming babies this time.
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* ''Manga/SleepyPrincessInTheDemonCastle'': Princess Syalis uses a magic item to de-age herself into a child so that she can convince the demons to coddle her to sleep. Unfortunately for her, a bakery in a nearby town is offering free samples that day, and nearly all the demons are gone, leaving only the three demons who are least suited to taking care of a child.
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That part doesn't fit the trope; she makes herself appear older, but the trope is about characters becoming younger.
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** The supernova Jewelry Bonney's Devil Fruit allows her to change the age of whoever she wants. Guess what she usually does when enemies get in her way? [[spoiler: It's revealed her most frequent target is herself, as she's actually twelve years old but makes herself appear to be in her twenties so as to avoid being caught by the World Government]].
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** The supernova Jewelry Bonney's Devil Fruit allows her to change the age of whoever she wants. Guess what she usually does when enemies get in her way? [[spoiler: It's revealed her most frequent target is herself, as she's actually twelve years old but makes herself appear to be in her twenties so as to avoid being caught by the World Government]].way?
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** The supernova Jewelry Bonney's Devil Fruit allows her to change the age of whoever she wants. Guess what she usually does when enemies get in her way?
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** The supernova Jewelry Bonney's Devil Fruit allows her to change the age of whoever she wants. Guess what she usually does when enemies get in her way?way? [[spoiler: It's revealed her most frequent target is herself, as she's actually twelve years old but makes herself appear to be in her twenties so as to avoid being caught by the World Government]].
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* ''Manga/WitchWatch'': [[spoiler:After Morihito is shot and nearly dies, Nico saves him by sacrificing her time. This heals him, but she turns into a young child as a result.]]
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** Not unlike ''GT'', the premise of ''Anime/DragonBallDaima'' has not just Goku but most of his friends de-aged into children (or babies in Goten, Trunks and Marron's case).
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* The Nehellenia story is reused in ''Manga/MermaidMelodyPichiPichiPitch'', but with Michal, the SicklyAndDelicate not-quite-villain.
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* The Nehellenia story is reused in ''Manga/MermaidMelodyPichiPichiPitch'', but with Michal, the SicklyAndDelicate DelicateAndSickly not-quite-villain.
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* Happens briefly in an episode of ''Anime/MagicalWarfare'', where Kurumi's crying ends up turning her into a baby. However, this doesn't last long, as she's back to normal the next scene we see her.
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* Happens This happens briefly in an episode of ''Anime/MagicalWarfare'', where the ''Literature/MagicalWarfare'' anime when Kurumi's crying ends up turning her into a baby. However, this doesn't last long, as she's back to normal the next scene we see her.
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* The plot of ''Manga/OneOperationJoker'' is kicked off when ComicBook/{{Batman}} falls into the same vat of chemicals ComicBook/TheJoker did, and is turned into a baby.
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* The plot of ''Manga/OneOperationJoker'' is kicked off when ComicBook/{{Batman}} falls into the same vat of chemicals ComicBook/TheJoker did, the Joker did and is turned into a baby.
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* Happens briefly in an episode of ''LightNovel/MagicalWarfare'', where Kurumi's crying ends up turning her into a baby. However, this doesn't last long, as she's back to normal the next scene we see her.
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* Happens briefly in an episode of ''LightNovel/MagicalWarfare'', ''Anime/MagicalWarfare'', where Kurumi's crying ends up turning her into a baby. However, this doesn't last long, as she's back to normal the next scene we see her.
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* This is the premise of the ''Kako Random'' arc of ''LightNovel/KokoroConnect''. The heroes find themselves randomly regressing to preteens or young children between 12:00 and 17:00, both physically and mentally. Interestingly, this also causes them to regain some of the memories they had at those ages. This is the work of Number Two, and once the latter's involvement is revealed, the regressions become even more random; lasting from a couple of seconds to almost a full day, and/or going all the way back to infancy.
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* This is the premise of the ''Kako Random'' arc of ''LightNovel/KokoroConnect''.''Literature/KokoroConnect''. The heroes find themselves randomly regressing to preteens or young children between 12:00 and 17:00, both physically and mentally. Interestingly, this also causes them to regain some of the memories they had at those ages. This is the work of Number Two, and once the latter's involvement is revealed, the regressions become even more random; lasting from a couple of seconds to almost a full day, and/or going all the way back to infancy.
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Trope has been merged with Old Maid.
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* ''Manga/BlackLagoon'': a non-{{canon}} {{omake}} has the main cast regress to adolescence and, in [[BloodKnight Balalaika's]] case, beyond. For the record, [[TokenMiniMoe loli-Balalaika]] is the cutest thing ever. The most shocking ones are Yolanda (the old nun), who was a delicious and ''hot'' [[ChristmasCake cake]] at 29 and Balalaika's underling Boris, who was {{Bishounen}} to the max.
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* ''Manga/BlackLagoon'': a non-{{canon}} {{omake}} has the main cast regress to adolescence and, in [[BloodKnight Balalaika's]] case, beyond. For the record, [[TokenMiniMoe loli-Balalaika]] mini-Balalaika]] is the cutest thing ever. The most shocking ones are Yolanda (the old nun), who was a delicious and downright ''hot'' [[ChristmasCake cake]] at 29 and Balalaika's underling Boris, who was {{Bishounen}} to the max.
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* In a chapter of the Japan-exclusive ''VideoGame/HyperdimensionNeptunia'' manga (Part of said chapter can be seen [[http://visibletime.ararchive.com/_Anim-Hyperdimension_Neptunia2_.jpg here]]), this happens to Nepgear, Rom and Ram, and Uni, who regress into babies after eating some pills that Neptune accidentally gave them. Of course, Neptune has a pretty hard time looking after them, until Gust gave her the pills to change the girls back.
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* In a chapter of the Japan-exclusive ''VideoGame/HyperdimensionNeptunia'' manga (Part of said chapter can be seen [[http://visibletime.ararchive.com/_Anim-Hyperdimension_Neptunia2_.jpg here]]), manga, this happens to Nepgear, Rom and Ram, and Uni, who regress into babies after eating some pills that Neptune accidentally gave them. Of course, Neptune has a pretty hard time looking after them, until Gust gave her the pills to change the girls back.
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* The Nehellenia story is reused in ''Manga/MermaidMelodyPichiPichiPitch'', but with Michal, the IllGirl and not-quite-villain.
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* The Nehellenia story is reused in ''Manga/MermaidMelodyPichiPichiPitch'', but with Michal, the IllGirl and SicklyAndDelicate not-quite-villain.
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[[FountainOfYouth Fountains of Youth]] in {{Anime}} and {{Manga}}.
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* ''Manga/The100GirlfriendsWhoReallyReallyReallyReallyReallyLoveYou'':
** In chapter 28, all the girls except Hakari are temporarily turned into babies thanks to one of Kusuri's drugs.
** Chapter 75 introduces Kusuri's grandmother Yaku, who took a prototype of Kusuri's immortality drug and permanently gained an 8 year old body.
** Chapter 84 is an invoked repeat of chapter 28, with Hakari and the girlfriends who had been introduced since becoming babies this time.
* Because [[PhlebotinumBreakdown Heaven's computer crashed]], this happened to Urd for about two chapters in the ''Manga/AhMyGoddess'' manga (and one episode of the 2005 animé), with [[OvernightAgeUp the reverse happening]] for youngest sister Skuld. Fortunately, she was able to get an interesting advantage out of it.
* In an episode of ''Manga/AkazukinChacha'', the main trio is tricked by some bad guys into drinking rejuvenation potion, and turn back into babies. Seravy and Dorothy are also reverted to kids. Of course, they all turn back at the end.
* A plot used multiple times in ''Literature/{{Anpanman}}''. A couple episodes have had Baikinman make a spray that changes anyone (or anything) in contact with it into babies (with objects becoming earlier stages, like a tree becoming a sapling). He does this as ways to make Anpanman weak against him, but it always gets foiled in the end. One theatrical short showed there's an entire lake, one side red, which turns the victim into a baby, the other side blue, which returns them to normal. Another theatrical short had Hiyariko, an aspiring scientist, create a potion to make Baikinman stronger...only to turn him into a baby. When he runs off, she makes what she thinks is an antidote, and sprays it all around the town...only to turn the entire town into babies. Thankfully, this potion was only temporary, and everyone returned to normal eventually on their own.
* In ''Manga/BlackCat'', [[BigBad Creed]] ([[MadScientist Doctor]] did in the anime instead) accidentally shoots Train with a Lucifer bullet, causing Train to transform back into a child (around 8 years old). It only lasts one episode (or a few chapters).
* ''Manga/BlackLagoon'': a non-{{canon}} {{omake}} has the main cast regress to adolescence and, in [[BloodKnight Balalaika's]] case, beyond. For the record, [[TokenMiniMoe loli-Balalaika]] is the cutest thing ever. The most shocking ones are Yolanda (the old nun), who was a delicious and ''hot'' [[ChristmasCake cake]] at 29 and Balalaika's underling Boris, who was {{Bishounen}} to the max.
* In ''Manga/{{Bleach}}'', [[spoiler:Neliel Tu Oderschvank]] originally had the appearance of a late teenager/young woman, but after being attacked [[spoiler:by her rival Nnoitra and having him crack her Hollow mask,]] she ended up reverting into a small child. Later [[spoiler: Urahara]] uses his devices to let her return to her original age.
* In an episode of ''Anime/BrigadoonMarinAndMelan'', Marine eats some weird chocolate [[MushroomSamba that causes her to start hallucinating]]. Among other things, she imagines herself [[OvernightAgeUp growing into a young adult]], then regressing into a baby.
* Who can ever forget [=APTX-4869=] in ''Manga/CaseClosed''? It regressed Shinichi Kudo and Shiho Miyano's ''body'' by around ten years, causing two {{Teen Genius}}es to live in first graders' bodies. On the other hand, [=APTX-4869=] [[MillionToOneChance is employed as a poison and is generally successful]].
* In the early chapters of ''Manga/ChronosRuler'', a teacher in her forties wished to one of the Horologues to get her youth back, and by the start of the series looks like a young woman. Too bad for her, she ends up becoming ''too'' young the next day; after she turned into a child, she tried to approach the Horologue in question to ger her time back, only for the Horologue to quickly suck out the ''rest'' of it, regressing her out of existence. This serves as a dire introduction to those demons' true nature.
* Played straight then subverted in the fourth episode of ''Anime/{{Classicaloid}}''. When Schubert starts playing his music, everyone else present shrinks out of their clothes as they regress into babies frolicking to and fro, but it soon turns out that they're actually perfectly normal, and that the music merely caused them to ''act'' like babies.
* Amber from ''Anime/DarkerThanBlack'' has this as her [[PowerAtAPrice remuneration]]; she regresses in age every time that she uses her powers. [[spoiler:In the end, she ends up fading into nothingness altogether due to overuse.]]
* In ''Manga/DeathNote'', Shinigami can steal the lifespans of humans by writing their names in Death Notes, which kills the human. Humans who use the Death Notes don't get the lifespans of their victims but if a Shinigami uses their Death Note to save a human's life, the Shinigami dies and the human gets all of their lifespan.
* One of the first monsters in ''Manga/DevilAndDevil'' is a huge tentacled... thing, that sucks time out of people. It turned a young woman and two young girls into babies, and a third young girl into a child, but they all turned back to normal when it got its ass handed to it by Sword.
* ''Manga/{{Doraemon}}'':
** This is one of the Time Cloth's main functions; one of its sides makes everything and everyone who gets wrapped in it younger. Gian ends up briefly turning into a baby because of it in its first appearance. In a later episode of the second anime, Nobita's mom is temporarily turned back into a child around her son's age, taking advantage of it to try and find a secret he's been hiding from her.
** ''Anime/DoraemonNobitaInTheWanNyanSpacetimeOdyssey'' follows the story of Eiji, an anthropomorphic dog who travels across time to find his ex-owner, Nobita, but the unstable time tunnel causes him to warp into another place and ended up being turned back into an infant. This also happens later with Gian and Suneo, but only temporarily.
* ''Franchise/DragonBall'':
** King Piccolo and [[Anime/DragonBallZLordSlug Lord Slug]] used the titular MacGuffin to restore their youth, putting their power at prime. Roshi and his sister Baba actually drank from a Fountain of Youth, which, rather than restore their youth, fixed them at that age, unable to die from old age.
** Goku turning into a child is part of the whole ''concept'' of ''Anime/DragonBallGT''.
** The concept was used again in the 2013 film ''Anime/DragonBallZBattleOfGods'' where the [[GoldfishPoopGang Pilaf Gang]] were transformed into children off-screen. This still holds true in ''Anime/DragonBallSuper'', to the point that in a BadFuture shown in ''Super'', Mai has merely grown back into her teens/early twenties instead of her original age.
** In ''Anime/DragonBallSuperBroly'', Bulma planned to use the Dragon Balls to wish to be 5 years younger, and is implied to have done this before.
* In ''Anime/ExpelledFromParadise'', Angela Balzack has spent her whole life since infancy digitized, living in a virtual world with 98% of humanity in the same boat. She's also Third Officer for System Security. When a real-world hacker potentially threatens the peace and stability of that virtual world, DEVA, she has to go out into the real world. One problem: her original body is long dead. Fortunately, the machines that run DEVA always save a DNA sample of every infant they digitize, in case of just such an emergency, so that they can clone new bodies, and uses age-accelerating incubation pods. However, Angela wants to get the jump on all the other agents being sent into the real world, so she cuts her new body's incubation period short, leaving her body at age 16 instead of... whatever age she is chronologically (we don't actually know). [[spoiler:She eventually gets trapped in her teenage body when she rebels against DEVA's cruel and oppressive government. Come on, they deleted ROCK AND ROLL!!!]]
* In ''Manga/FairyTail'', a villain in the Village of the Sun arc named Doriath uses magic that severely weakens people's magical and physical power, and has the added effect of turning them into children. Erza, Natsu, and Gray are hit by it but turned back to normal later. Also, everyone present is regressed briefly in chapter 350 (including Wendy, who becomes an even younger child).
* In ''Manga/FourKnightsOfTheApocalypse'', Ardbeg's Reverse ability allows him to [[ExactlyWhatItSaysOnTheTin reverse]] the age of every living thing within a certain radius, rejuvenating them to infancy.
* ''[[BodyHorror Horrifically]]'' deconstructed in ''Manga/FrankenFran'': The villain from the "Eternal Youth" chapter is an old woman who wishes to regain her youth, but kills many doctors and steals their researches to do so. When comes Fran's turn, it comes back to bite her really hard: [[spoiler:At first, it works and she becomes a young woman again, but because Fran's research was still very experimental, she soon afterwards turns into a pulsating mess of cancer cells.]]
* In ''Manga/FushigiYuugi'', the trope is invoked when [[spoiler: the TimeMaster [[NeverMessWithGranny Subaru]] briefly uses her powers on herself and her husband [[CoolOldGuy Tokaki]] so [[BattleCouple they]] can help Miaka and the Suzaku Seishi.]]
* In ''Manga/GakkouKaidan'' (a Yousuke Takahashi manga that's [[JustForFun/IThoughtItMeant unrelated to the anime]] ''Anime/GhostStories''), a VillainousHarlequin transforms a young girl into a baby and a young female teacher into a kid. Both turn back to normal when the harlequin gets his ass kicked.
* In the episode "Ultra Hot Kid's Meal" of ''[[Anime/GalaxyAngel Galaxy Angel A]]'', the Angel Brigade mistakes a Lost Technology for a box of uirÅ and turn into children, toddlers, and in Milfeulle's case, a baby. Because TheMindIsAPlaythingOfTheBody, the girls gave the twins a pretty hard time looking after them.
* The Korean manhwa series ''Manhwa/HorrorCollector'' depicts UsefulNotes/ElizabethBathory as a young adult who frequently reverts back to her teenage self through her regular {{Blood Bath}}s.
* In a chapter of the Japan-exclusive ''VideoGame/HyperdimensionNeptunia'' manga (Part of said chapter can be seen [[http://visibletime.ararchive.com/_Anim-Hyperdimension_Neptunia2_.jpg here]]), this happens to Nepgear, Rom and Ram, and Uni, who regress into babies after eating some pills that Neptune accidentally gave them. Of course, Neptune has a pretty hard time looking after them, until Gust gave her the pills to change the girls back.
* ''Manga/IchinenseiNiNacchattara'' has this as part of its core concept, with main character Iori going from high school to elementary school, and getting [[GenderBender gender-bent]] in the process. However, he retains his original personality, and he's not happy about becoming an elementary school girl. Later on, [[spoiler: almost the entire town regresses into kids. This causes mass hysteria across the city since the rejuvenation virus was rather contagious, but since Iori held the antibody, everyone was later returned to normal]].
* An episode of ''Anime/JewelpetSunshine'' involves Labra transforming almost everyone in the Plum class into babies after being teased for being a baby. The ones who were aged back into infants were Ruby, Sapphie, Garnet, Peridot, Gakuto, Yaginuma, and even Mikage.
* ''Manga/JojosBizarreAdventureStardustCrusaders''' Alessi does this to opponents with his [[FightingSpirit Stand]], Sethan. The longer a person stands in his shadow ([[LivingShadow through which Sethan manifests]]), the younger they get, including their Stand getting weaker, and that's only if the victim developed their Stand at a young age. In one instance he's able to turn a grown woman into a fetus, but when he tries this on Jotaro, he learns the hard way that [[BroughtDownToBadass Jotaro could still easily clobber him, even as a seven-year-old]].
* In ''Manga/KoiKoi7'', after Yayoi Asuka ([[EyepatchOfPower the one with the eyepatch]]) goes berserk, she's rebooted in one of Otome's spare bodies as a cute young girl named Gantai-chan who doesn't remember much of what happened before.
* This is the premise of the ''Kako Random'' arc of ''LightNovel/KokoroConnect''. The heroes find themselves randomly regressing to preteens or young children between 12:00 and 17:00, both physically and mentally. Interestingly, this also causes them to regain some of the memories they had at those ages. This is the work of Number Two, and once the latter's involvement is revealed, the regressions become even more random; lasting from a couple of seconds to almost a full day, and/or going all the way back to infancy.
* This is part of the premise of ''Manga/LivingForTheDayAfterTomorrow'': when they both happen to meet at the same time in front of a wishing stone, a young woman transforms into a little girl, and vice-versa. It is implied they change back at the end of the series.
* In episode 19 of ''[[Theatre/TheBlueBird Maeterlinck's Blue Bird: Tyltyl and Mytyl's Adventurous Journey]]'', the animated adaptation of ''Theatre/TheBlueBird'', the titular children and their pets are transformed into babies by the villain's powers. The spirits have to watch over them while Berylude turns herself into a young and powerful warrior to fight the villain and return them to normal.
* In ''Manga/MagicalGirlLyricalNanohaVivid'', [[spoiler:one of Fabian's devils]] has a spell that de-ages the target and successfully enchants [[spoiler:[[OneManArmy Sieglinde]]]] with it to incapacitate her.
* In an episode of ''[[Anime/PrettySammy Magical Project S]]'', this happens to Sasami as an after-effect of an aging potion. The aging initially works well, but after Sasami returns to her normal age, she turns into a baby overnight.
* Happens briefly in an episode of ''LightNovel/MagicalWarfare'', where Kurumi's crying ends up turning her into a baby. However, this doesn't last long, as she's back to normal the next scene we see her.
* In episode 3 ''Manga/MamotteLollipop'', Rokka temporarily transforms Nina into a baby out of jealousy.
* ''Manga/{{MAR}}'': [[spoiler: This is what happens to Loco every time she uses her powers. By the time she's introduced, she looks like a child of around 11 or 12, despite actually being 32 years old. She eventually turns back into a baby after a HeroicSacrifice, and is being taken care of by Chaton and Alan near the end of the series]].
* ''Manga/MarvelousMelmo'': Nine-year-old Melmo's magical pills allow her to change her age as she pleases. Depending on the situation, she can change herself into a baby, a nineteen-year-old girl, or even [[VoluntaryShapeshifting regress back into a fetus in order to be reborn as an animal]], should she need to.
* This is basically the point of ''Mayonaka Lolita'': Mishiru Kachiwabara, a very beautiful young girl, is given a strange juice by a male student (Aoi Makimura) she had never seen before. As it turns out, that juice is a rejuvenation potion, which their teacher had mistakenly given to Aoi as juice, and Mishiru regresses into a little girl. Her teacher tells her the only way to get back to normal is to kiss the person she loves, but tough luck, Mishiru doesn't love anybody. Because she can't go back home as a child, Aoi brings her to his house and allows her to stay there. [[spoiler:They eventually do kiss at the end of the first chapter, and Michiru turns back to normal... before turning into a child again.]]
* The Nehellenia story is reused in ''Manga/MermaidMelodyPichiPichiPitch'', but with Michal, the IllGirl and not-quite-villain.
* In ''Manga/NegimaMagisterNegiMagi'', WeaselMascot Chamo produces a jar of magical (and illegal) candy that can produce this effect as a sort of illusion (red candy [[OvernightAgeUp for older]], blue for this) both for fun on the part of the girls and as a StrangelyEffectiveDisguise when they [[ClearMyName become wanted people]]. It's been implied that TheMindIsAPlaythingOfTheBody, resulting in the aged-down characters acting with far lower maturity than usual, though they retain their intelligence. This doesn't work both ways, so their [[TheCutie adult forms behave like giddy teens]].
* In ''Anime/OnegaiMyMelody'', one music teacher wishes his best student would go back to his younger, happier days. Kuromi grants his wish, but Hiiragi overpowers and scatters the spell. Across town, everyone from middle school-age up is turned into kids, throwing the town into chaos.
* The plot of ''Manga/OneOperationJoker'' is kicked off when ComicBook/{{Batman}} falls into the same vat of chemicals ComicBook/TheJoker did, and is turned into a baby.
* ''Manga/OnePiece'':
** The supernova Jewelry Bonney's Devil Fruit allows her to change the age of whoever she wants. Guess what she usually does when enemies get in her way?
** From the twelfth movie ''Anime/OnePieceFilmZ'', Ain's Modo Modo no Mi powers allow her to rejuvenate her opponents. Unlike Bonney's powers, however, it works on inanimate objects too, and it can only work backwards, whereas Bonney can also age her opponents. [[spoiler:Nami, Chopper, Robin, and Brook all got hit by it, regressing the former two into children, Robin into a teenager, and... not altering Brook's physical appearance at all, [[DemBones since he's a skeleton]].]]
** Nightin from the ''3D2Y'' TV special is an [[{{Gonk}} ugly]] and [[MiniatureSeniorCitizen short]] 80-year old woman, but by using medicine of her own conception, she can rejuvenate herself into a much more beautiful young woman.
* [[spoiler:Jack Vessalius]] has this happen to him in ''Manga/PandoraHearts'' as a result of being rejected by the Abyss. [[spoiler:His soul was shattered to pieces during the fight between Alice, Alyss and the Core of the Abyss. As a result, he kept on de-aging in a cycle: every time he reached the age of twenty-five, he will become younger and younger. Jack's mind has disappeared almost entirely due to a result, leaving only B-rabbit!Oz in place of him, who, according to the manga: "Had lost all of his memories and his powers and fell in a deep slumber."]]
* In episode 90 of ''Anime/PokemonJourneysTheSeries'', a clash between [[TimeMaster Dialga]] and [[SpaceMaster Palkia]] is throwing space and time out of whack. Dialga's powers are reversing the time of Pokémon and humans alike, making them younger until Pokémon turn into eggs and humans turn into young children. The heroes and their alternate universe selves were affected as well, but managed to stop the legendaries' fight before any irrepairable damage could be done, turning everyone and everything back to normal.
* ''Anime/PrettyCure''
** In an episode of ''Anime/SmilePrettyCure'', the main heroines are turned into kids and need to find a way to turn back.
** The same scenario happens again in ''Anime/MahoGirlsPreCure'', albeit with obviously different protagonists this time.
* ''Manga/RanmaOneHalf'':
** Lukkosai, who tried to use the spring of drowned child to regain his youth, but instead just goes from way too old to way too young (both [[MiniatureSeniorCitizens about the same size]]). He then uses this form to get revenge on Happo while pretending to be his own grandson.
** Another story involved mushrooms that change your age in years to their length in centimeters. Ryoga eats a short one and then makes Ranma eat one. They spend most of the chapter trying to change back by growing mushrooms big enough to return them to their normal ages, while constantly sabotaging each others' mushrooms.
** And yet another story from the manga has Happosai feeling the pangs of old age. He finds out about a potion that will restore his youth, but first he needs the tears of a beast that is both male and female. The next thing you know, tear gas and onions fly liberally around Ranma. When he finally succeeds (by poking a pressure point that makes Ranma [[OcularGushers gush out tears like a firehose]]) he trips, and splashes the tears all over the floor. Kasumi wipes them up with a rag, but since it had been used to clean up soy sauce, the resulting potion regresses Happosai's ''mind'' to that of a baby.
* ''Franchise/SailorMoon'':
** [[Anime/SailorMoon The anime]] has several examples. In the end of the third season (''Sailor Moon S''), Hotaru, after sacrificing herself to save the world, is brought back as an infant with no memories of her previous life. In the fourth season (''Sailor Moon [=SuperS=]''), [=PallaPalla=] casts a spell on Usagi and Chibiusa that briefly exchange their ages for one episode - causing havoc as Chibiusa, having fulfilled her dream of becoming a beautiful adult, is now unable to summon Pegasus and Sailor Moon can't defeat the Lemures without him. In the beginning of the fifth season (''Sailor Moon Stars''), Hotaru [[PlotRelevantAgeUp rapidly grows back]] as her memories return, and the previous season's BigBad, Nehellenia, is returned to childhood to allow her to relive her life and avoid the mistakes that turned her into a villain in the first place.
** In the [[Manga/SailorMoon manga]], [=PallaPalla=] swaps Usagi and Chibiusa's in the first chapter of the Dream arc, which is actually done to depower the two of them. They eventually overcome it and transform into their proper bodies using their henshin phrases. Later in the same arc, Zirconia depowers both Sailor Moon and Tuxedo Mask in the same manner, turning them into six-year-olds and preventing them from accessing their magic. Pegasus reverses it by transporting them to Elysion, which has enough purifying power to break the spell.
* ''Manga/RosarioPlusVampire'' has an example of this one. [[TokenMiniMoe Yukari and Kokoa]], after realizing that they're not being taken seriously due to their age, use some of Yukari's age-up pills for a [[OvernightAgeUp temporary change]]. When the pills wear off, Kokoa finds herself ''younger'' than before. She finds herself in trouble shortly thereafter, only to be saved by the entire UnwantedHarem (sans Tsukune) turned into children along with her. Much cuteness and butt-kicking ensue.
* Episode 9 of ''Manga/SgtFrog'' features mother Aki Hinata getting turned into a teenager by Kururu's newest invention. In a later episode, the same gun turns Fuyuki into a kindergartner. Even later, Natsumi, Keroro, Giroro, and Kururu also get zapped by this gun. [[spoiler:In one episode, the entire planet gets zapped by this gun, setting time back by about twenty years.]]
* Happened in ''Manga/SketDance'':
** The first time was with Bossun after accidentally drinking Chuu-san's youth potion, mistaking it for a bottle of cola. Himeko [[CutenessProximity absolutely flips over him]].
** The second time was with Himeko and Momoka, several chapters later, at the same time, with the ''same bottle of cola''. Suffice to say, Bossun had a swell time looking after them.
** In the anime, two girls from the student council drink it on purpose, because "life is an adventure". Needless to say, it makes things even harder. In both versions, when the rejuvenated girls drink the antidote, they get ten years older than normal. And of course, by the time the next episode starts, [[UnexplainedRecovery they're back to their normal ages again]].
** Happened for the third time in Chapter 239, with [[TheRival Tsubaki]]. Except this time he reverted both in physical ''and'' mental state. Everyone, including Bossun and Daisy, gushes over [[CutenessProximity how cute he is]].
* Mosquito from ''Anime/SoulEater'' weaponizes this, being able to regress to any point in his extremely long life, which combined with his bizarre, chaotic life cycle gives him plenty of forms to change into, from a comically buff gorilla man to an elongated insectoid, to a humanoid vampire-esque figure, to an amorphous EldritchAbomination.
* In ''Anime/{{Stitch}}'', Babyfier (a creature that can turn people into babies) makes 3 appearances.
** In "Rivals stick Together" Babyfier is unleashed at a school turning most of the students and adults into babies.
** In another episode Babyfier turns the main character and her friends into toddlers.
** In the third episode, Babyfier is now good and turns a couple of the villains into babies.
* ''Manga/TheSevenDeadlySins'':
** The setting has a literal fountain of youth that makes the drinker immortal if they drink the entire fountain (which is just a cup). This is how Ban gained his immortality.
* Washu did this to herself in the ''Anime/TenchiMuyo'' OVA. [[spoiler:She was so distraught from her husband using his higher prestige to take away her child and leave her, she used her super-science to reverse her physical age to that of a 12-year-old so she'd never suffer that sort of heartbreak again. She can return at any time and explicitly says she'll do it if Tenchi'll have a child with her. Ryoko is not amused.]]
* Some chapters/episodes of ''Manga/ToLoveRu'' and the ''To-Love-Ru Darkness'' OVA feature a creature named the "skunk of youth", which regresses some of the main characters, among others, into kids.
** A trait of Lala's species is that if they exert too much energy, their bodies shrink to a younger state. This happens to her when she tries to stop Yami after being overtaken by her "Darkness" form, where she expends too much energy and shrinks to the size of a little girl.
* ''Manga/TheWorldGodOnlyKnows'':
** In the "Heart of Jupiter" arc, [[spoiler: Keima is sent back to the past via MentalTimeTravel and given a mission to save a cute but emotionless and mysterious young girl from committing suicide. If she gets overtaken by despair, she starts getting younger until she's transformed into a baby, which triggers a ResetButton that sends Keima back to the start of the mission. However, he can stop her from getting younger by kissing her before she turns into a baby]].
** The main manga also had a three-chapter spinoff called ''Magical Star Kanon 100%'', focused on, as the name implies, Kanon Nakagawa. In it, she is turned into a child by a Runaway Spirit and has to hide her identity and find a way to get back to her true age. The OVA version even has Elsie turn back into a child.
* In ''Manga/YuunaAndTheHauntedHotSprings'', the landlady's collection includes water from the Fountain of Youth that makes those who get splashed with it turn younger in body and mind. Nadare Tenko uses it in the "Yukemori Targeted Arc" to make everyone in the main cast younger.
* In the Dark Tournament arc of ''Manga/YuYuHakusho'', Ura Urashima uses a special mist meant to de-age its victims past the point of conception. Unfortunately for him, his target was Kurama, and once his human body went into non-existence, his previous incarnation - full-powered demon Yokokurama - manifested. Ura is so freaked out that it's Kurama rather than someone just using his name [[spoiler:his team captain]] has to [[https://www.youtube.com/watch?v=obfeTl5_S18 kill him]] to keep him from spilling all the beans.
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[[FountainOfYouth Fountains of Youth]] in {{Anime}} and {{Manga}}.
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* ''Manga/The100GirlfriendsWhoReallyReallyReallyReallyReallyLoveYou'':
** In chapter 28, all the girls except Hakari are temporarily turned into babies thanks to one of Kusuri's drugs.
** Chapter 75 introduces Kusuri's grandmother Yaku, who took a prototype of Kusuri's immortality drug and permanently gained an 8 year old body.
** Chapter 84 is an invoked repeat of chapter 28, with Hakari and the girlfriends who had been introduced since becoming babies this time.
* Because [[PhlebotinumBreakdown Heaven's computer crashed]], this happened to Urd for about two chapters in the ''Manga/AhMyGoddess'' manga (and one episode of the 2005 animé), with [[OvernightAgeUp the reverse happening]] for youngest sister Skuld. Fortunately, she was able to get an interesting advantage out of it.
* In an episode of ''Manga/AkazukinChacha'', the main trio is tricked by some bad guys into drinking rejuvenation potion, and turn back into babies. Seravy and Dorothy are also reverted to kids. Of course, they all turn back at the end.
* A plot used multiple times in ''Literature/{{Anpanman}}''. A couple episodes have had Baikinman make a spray that changes anyone (or anything) in contact with it into babies (with objects becoming earlier stages, like a tree becoming a sapling). He does this as ways to make Anpanman weak against him, but it always gets foiled in the end. One theatrical short showed there's an entire lake, one side red, which turns the victim into a baby, the other side blue, which returns them to normal. Another theatrical short had Hiyariko, an aspiring scientist, create a potion to make Baikinman stronger...only to turn him into a baby. When he runs off, she makes what she thinks is an antidote, and sprays it all around the town...only to turn the entire town into babies. Thankfully, this potion was only temporary, and everyone returned to normal eventually on their own.
* In ''Manga/BlackCat'', [[BigBad Creed]] ([[MadScientist Doctor]] did in the anime instead) accidentally shoots Train with a Lucifer bullet, causing Train to transform back into a child (around 8 years old). It only lasts one episode (or a few chapters).
* ''Manga/BlackLagoon'': a non-{{canon}} {{omake}} has the main cast regress to adolescence and, in [[BloodKnight Balalaika's]] case, beyond. For the record, [[TokenMiniMoe loli-Balalaika]] is the cutest thing ever. The most shocking ones are Yolanda (the old nun), who was a delicious and ''hot'' [[ChristmasCake cake]] at 29 and Balalaika's underling Boris, who was {{Bishounen}} to the max.
* In ''Manga/{{Bleach}}'', [[spoiler:Neliel Tu Oderschvank]] originally had the appearance of a late teenager/young woman, but after being attacked [[spoiler:by her rival Nnoitra and having him crack her Hollow mask,]] she ended up reverting into a small child. Later [[spoiler: Urahara]] uses his devices to let her return to her original age.
* In an episode of ''Anime/BrigadoonMarinAndMelan'', Marine eats some weird chocolate [[MushroomSamba that causes her to start hallucinating]]. Among other things, she imagines herself [[OvernightAgeUp growing into a young adult]], then regressing into a baby.
* Who can ever forget [=APTX-4869=] in ''Manga/CaseClosed''? It regressed Shinichi Kudo and Shiho Miyano's ''body'' by around ten years, causing two {{Teen Genius}}es to live in first graders' bodies. On the other hand, [=APTX-4869=] [[MillionToOneChance is employed as a poison and is generally successful]].
* In the early chapters of ''Manga/ChronosRuler'', a teacher in her forties wished to one of the Horologues to get her youth back, and by the start of the series looks like a young woman. Too bad for her, she ends up becoming ''too'' young the next day; after she turned into a child, she tried to approach the Horologue in question to ger her time back, only for the Horologue to quickly suck out the ''rest'' of it, regressing her out of existence. This serves as a dire introduction to those demons' true nature.
* Played straight then subverted in the fourth episode of ''Anime/{{Classicaloid}}''. When Schubert starts playing his music, everyone else present shrinks out of their clothes as they regress into babies frolicking to and fro, but it soon turns out that they're actually perfectly normal, and that the music merely caused them to ''act'' like babies.
* Amber from ''Anime/DarkerThanBlack'' has this as her [[PowerAtAPrice remuneration]]; she regresses in age every time that she uses her powers. [[spoiler:In the end, she ends up fading into nothingness altogether due to overuse.]]
* In ''Manga/DeathNote'', Shinigami can steal the lifespans of humans by writing their names in Death Notes, which kills the human. Humans who use the Death Notes don't get the lifespans of their victims but if a Shinigami uses their Death Note to save a human's life, the Shinigami dies and the human gets all of their lifespan.
* One of the first monsters in ''Manga/DevilAndDevil'' is a huge tentacled... thing, that sucks time out of people. It turned a young woman and two young girls into babies, and a third young girl into a child, but they all turned back to normal when it got its ass handed to it by Sword.
* ''Manga/{{Doraemon}}'':
** This is one of the Time Cloth's main functions; one of its sides makes everything and everyone who gets wrapped in it younger. Gian ends up briefly turning into a baby because of it in its first appearance. In a later episode of the second anime, Nobita's mom is temporarily turned back into a child around her son's age, taking advantage of it to try and find a secret he's been hiding from her.
** ''Anime/DoraemonNobitaInTheWanNyanSpacetimeOdyssey'' follows the story of Eiji, an anthropomorphic dog who travels across time to find his ex-owner, Nobita, but the unstable time tunnel causes him to warp into another place and ended up being turned back into an infant. This also happens later with Gian and Suneo, but only temporarily.
* ''Franchise/DragonBall'':
** King Piccolo and [[Anime/DragonBallZLordSlug Lord Slug]] used the titular MacGuffin to restore their youth, putting their power at prime. Roshi and his sister Baba actually drank from a Fountain of Youth, which, rather than restore their youth, fixed them at that age, unable to die from old age.
** Goku turning into a child is part of the whole ''concept'' of ''Anime/DragonBallGT''.
** The concept was used again in the 2013 film ''Anime/DragonBallZBattleOfGods'' where the [[GoldfishPoopGang Pilaf Gang]] were transformed into children off-screen. This still holds true in ''Anime/DragonBallSuper'', to the point that in a BadFuture shown in ''Super'', Mai has merely grown back into her teens/early twenties instead of her original age.
** In ''Anime/DragonBallSuperBroly'', Bulma planned to use the Dragon Balls to wish to be 5 years younger, and is implied to have done this before.
* In ''Anime/ExpelledFromParadise'', Angela Balzack has spent her whole life since infancy digitized, living in a virtual world with 98% of humanity in the same boat. She's also Third Officer for System Security. When a real-world hacker potentially threatens the peace and stability of that virtual world, DEVA, she has to go out into the real world. One problem: her original body is long dead. Fortunately, the machines that run DEVA always save a DNA sample of every infant they digitize, in case of just such an emergency, so that they can clone new bodies, and uses age-accelerating incubation pods. However, Angela wants to get the jump on all the other agents being sent into the real world, so she cuts her new body's incubation period short, leaving her body at age 16 instead of... whatever age she is chronologically (we don't actually know). [[spoiler:She eventually gets trapped in her teenage body when she rebels against DEVA's cruel and oppressive government. Come on, they deleted ROCK AND ROLL!!!]]
* In ''Manga/FairyTail'', a villain in the Village of the Sun arc named Doriath uses magic that severely weakens people's magical and physical power, and has the added effect of turning them into children. Erza, Natsu, and Gray are hit by it but turned back to normal later. Also, everyone present is regressed briefly in chapter 350 (including Wendy, who becomes an even younger child).
* In ''Manga/FourKnightsOfTheApocalypse'', Ardbeg's Reverse ability allows him to [[ExactlyWhatItSaysOnTheTin reverse]] the age of every living thing within a certain radius, rejuvenating them to infancy.
* ''[[BodyHorror Horrifically]]'' deconstructed in ''Manga/FrankenFran'': The villain from the "Eternal Youth" chapter is an old woman who wishes to regain her youth, but kills many doctors and steals their researches to do so. When comes Fran's turn, it comes back to bite her really hard: [[spoiler:At first, it works and she becomes a young woman again, but because Fran's research was still very experimental, she soon afterwards turns into a pulsating mess of cancer cells.]]
* In ''Manga/FushigiYuugi'', the trope is invoked when [[spoiler: the TimeMaster [[NeverMessWithGranny Subaru]] briefly uses her powers on herself and her husband [[CoolOldGuy Tokaki]] so [[BattleCouple they]] can help Miaka and the Suzaku Seishi.]]
* In ''Manga/GakkouKaidan'' (a Yousuke Takahashi manga that's [[JustForFun/IThoughtItMeant unrelated to the anime]] ''Anime/GhostStories''), a VillainousHarlequin transforms a young girl into a baby and a young female teacher into a kid. Both turn back to normal when the harlequin gets his ass kicked.
* In the episode "Ultra Hot Kid's Meal" of ''[[Anime/GalaxyAngel Galaxy Angel A]]'', the Angel Brigade mistakes a Lost Technology for a box of uirÅ and turn into children, toddlers, and in Milfeulle's case, a baby. Because TheMindIsAPlaythingOfTheBody, the girls gave the twins a pretty hard time looking after them.
* The Korean manhwa series ''Manhwa/HorrorCollector'' depicts UsefulNotes/ElizabethBathory as a young adult who frequently reverts back to her teenage self through her regular {{Blood Bath}}s.
* In a chapter of the Japan-exclusive ''VideoGame/HyperdimensionNeptunia'' manga (Part of said chapter can be seen [[http://visibletime.ararchive.com/_Anim-Hyperdimension_Neptunia2_.jpg here]]), this happens to Nepgear, Rom and Ram, and Uni, who regress into babies after eating some pills that Neptune accidentally gave them. Of course, Neptune has a pretty hard time looking after them, until Gust gave her the pills to change the girls back.
* ''Manga/IchinenseiNiNacchattara'' has this as part of its core concept, with main character Iori going from high school to elementary school, and getting [[GenderBender gender-bent]] in the process. However, he retains his original personality, and he's not happy about becoming an elementary school girl. Later on, [[spoiler: almost the entire town regresses into kids. This causes mass hysteria across the city since the rejuvenation virus was rather contagious, but since Iori held the antibody, everyone was later returned to normal]].
* An episode of ''Anime/JewelpetSunshine'' involves Labra transforming almost everyone in the Plum class into babies after being teased for being a baby. The ones who were aged back into infants were Ruby, Sapphie, Garnet, Peridot, Gakuto, Yaginuma, and even Mikage.
* ''Manga/JojosBizarreAdventureStardustCrusaders''' Alessi does this to opponents with his [[FightingSpirit Stand]], Sethan. The longer a person stands in his shadow ([[LivingShadow through which Sethan manifests]]), the younger they get, including their Stand getting weaker, and that's only if the victim developed their Stand at a young age. In one instance he's able to turn a grown woman into a fetus, but when he tries this on Jotaro, he learns the hard way that [[BroughtDownToBadass Jotaro could still easily clobber him, even as a seven-year-old]].
* In ''Manga/KoiKoi7'', after Yayoi Asuka ([[EyepatchOfPower the one with the eyepatch]]) goes berserk, she's rebooted in one of Otome's spare bodies as a cute young girl named Gantai-chan who doesn't remember much of what happened before.
* This is the premise of the ''Kako Random'' arc of ''LightNovel/KokoroConnect''. The heroes find themselves randomly regressing to preteens or young children between 12:00 and 17:00, both physically and mentally. Interestingly, this also causes them to regain some of the memories they had at those ages. This is the work of Number Two, and once the latter's involvement is revealed, the regressions become even more random; lasting from a couple of seconds to almost a full day, and/or going all the way back to infancy.
* This is part of the premise of ''Manga/LivingForTheDayAfterTomorrow'': when they both happen to meet at the same time in front of a wishing stone, a young woman transforms into a little girl, and vice-versa. It is implied they change back at the end of the series.
* In episode 19 of ''[[Theatre/TheBlueBird Maeterlinck's Blue Bird: Tyltyl and Mytyl's Adventurous Journey]]'', the animated adaptation of ''Theatre/TheBlueBird'', the titular children and their pets are transformed into babies by the villain's powers. The spirits have to watch over them while Berylude turns herself into a young and powerful warrior to fight the villain and return them to normal.
* In ''Manga/MagicalGirlLyricalNanohaVivid'', [[spoiler:one of Fabian's devils]] has a spell that de-ages the target and successfully enchants [[spoiler:[[OneManArmy Sieglinde]]]] with it to incapacitate her.
* In an episode of ''[[Anime/PrettySammy Magical Project S]]'', this happens to Sasami as an after-effect of an aging potion. The aging initially works well, but after Sasami returns to her normal age, she turns into a baby overnight.
* Happens briefly in an episode of ''LightNovel/MagicalWarfare'', where Kurumi's crying ends up turning her into a baby. However, this doesn't last long, as she's back to normal the next scene we see her.
* In episode 3 ''Manga/MamotteLollipop'', Rokka temporarily transforms Nina into a baby out of jealousy.
* ''Manga/{{MAR}}'': [[spoiler: This is what happens to Loco every time she uses her powers. By the time she's introduced, she looks like a child of around 11 or 12, despite actually being 32 years old. She eventually turns back into a baby after a HeroicSacrifice, and is being taken care of by Chaton and Alan near the end of the series]].
* ''Manga/MarvelousMelmo'': Nine-year-old Melmo's magical pills allow her to change her age as she pleases. Depending on the situation, she can change herself into a baby, a nineteen-year-old girl, or even [[VoluntaryShapeshifting regress back into a fetus in order to be reborn as an animal]], should she need to.
* This is basically the point of ''Mayonaka Lolita'': Mishiru Kachiwabara, a very beautiful young girl, is given a strange juice by a male student (Aoi Makimura) she had never seen before. As it turns out, that juice is a rejuvenation potion, which their teacher had mistakenly given to Aoi as juice, and Mishiru regresses into a little girl. Her teacher tells her the only way to get back to normal is to kiss the person she loves, but tough luck, Mishiru doesn't love anybody. Because she can't go back home as a child, Aoi brings her to his house and allows her to stay there. [[spoiler:They eventually do kiss at the end of the first chapter, and Michiru turns back to normal... before turning into a child again.]]
* The Nehellenia story is reused in ''Manga/MermaidMelodyPichiPichiPitch'', but with Michal, the IllGirl and not-quite-villain.
* In ''Manga/NegimaMagisterNegiMagi'', WeaselMascot Chamo produces a jar of magical (and illegal) candy that can produce this effect as a sort of illusion (red candy [[OvernightAgeUp for older]], blue for this) both for fun on the part of the girls and as a StrangelyEffectiveDisguise when they [[ClearMyName become wanted people]]. It's been implied that TheMindIsAPlaythingOfTheBody, resulting in the aged-down characters acting with far lower maturity than usual, though they retain their intelligence. This doesn't work both ways, so their [[TheCutie adult forms behave like giddy teens]].
* In ''Anime/OnegaiMyMelody'', one music teacher wishes his best student would go back to his younger, happier days. Kuromi grants his wish, but Hiiragi overpowers and scatters the spell. Across town, everyone from middle school-age up is turned into kids, throwing the town into chaos.
* The plot of ''Manga/OneOperationJoker'' is kicked off when ComicBook/{{Batman}} falls into the same vat of chemicals ComicBook/TheJoker did, and is turned into a baby.
* ''Manga/OnePiece'':
** The supernova Jewelry Bonney's Devil Fruit allows her to change the age of whoever she wants. Guess what she usually does when enemies get in her way?
** From the twelfth movie ''Anime/OnePieceFilmZ'', Ain's Modo Modo no Mi powers allow her to rejuvenate her opponents. Unlike Bonney's powers, however, it works on inanimate objects too, and it can only work backwards, whereas Bonney can also age her opponents. [[spoiler:Nami, Chopper, Robin, and Brook all got hit by it, regressing the former two into children, Robin into a teenager, and... not altering Brook's physical appearance at all, [[DemBones since he's a skeleton]].]]
** Nightin from the ''3D2Y'' TV special is an [[{{Gonk}} ugly]] and [[MiniatureSeniorCitizen short]] 80-year old woman, but by using medicine of her own conception, she can rejuvenate herself into a much more beautiful young woman.
* [[spoiler:Jack Vessalius]] has this happen to him in ''Manga/PandoraHearts'' as a result of being rejected by the Abyss. [[spoiler:His soul was shattered to pieces during the fight between Alice, Alyss and the Core of the Abyss. As a result, he kept on de-aging in a cycle: every time he reached the age of twenty-five, he will become younger and younger. Jack's mind has disappeared almost entirely due to a result, leaving only B-rabbit!Oz in place of him, who, according to the manga: "Had lost all of his memories and his powers and fell in a deep slumber."]]
* In episode 90 of ''Anime/PokemonJourneysTheSeries'', a clash between [[TimeMaster Dialga]] and [[SpaceMaster Palkia]] is throwing space and time out of whack. Dialga's powers are reversing the time of Pokémon and humans alike, making them younger until Pokémon turn into eggs and humans turn into young children. The heroes and their alternate universe selves were affected as well, but managed to stop the legendaries' fight before any irrepairable damage could be done, turning everyone and everything back to normal.
* ''Anime/PrettyCure''
** In an episode of ''Anime/SmilePrettyCure'', the main heroines are turned into kids and need to find a way to turn back.
** The same scenario happens again in ''Anime/MahoGirlsPreCure'', albeit with obviously different protagonists this time.
* ''Manga/RanmaOneHalf'':
** Lukkosai, who tried to use the spring of drowned child to regain his youth, but instead just goes from way too old to way too young (both [[MiniatureSeniorCitizens about the same size]]). He then uses this form to get revenge on Happo while pretending to be his own grandson.
** Another story involved mushrooms that change your age in years to their length in centimeters. Ryoga eats a short one and then makes Ranma eat one. They spend most of the chapter trying to change back by growing mushrooms big enough to return them to their normal ages, while constantly sabotaging each others' mushrooms.
** And yet another story from the manga has Happosai feeling the pangs of old age. He finds out about a potion that will restore his youth, but first he needs the tears of a beast that is both male and female. The next thing you know, tear gas and onions fly liberally around Ranma. When he finally succeeds (by poking a pressure point that makes Ranma [[OcularGushers gush out tears like a firehose]]) he trips, and splashes the tears all over the floor. Kasumi wipes them up with a rag, but since it had been used to clean up soy sauce, the resulting potion regresses Happosai's ''mind'' to that of a baby.
* ''Franchise/SailorMoon'':
** [[Anime/SailorMoon The anime]] has several examples. In the end of the third season (''Sailor Moon S''), Hotaru, after sacrificing herself to save the world, is brought back as an infant with no memories of her previous life. In the fourth season (''Sailor Moon [=SuperS=]''), [=PallaPalla=] casts a spell on Usagi and Chibiusa that briefly exchange their ages for one episode - causing havoc as Chibiusa, having fulfilled her dream of becoming a beautiful adult, is now unable to summon Pegasus and Sailor Moon can't defeat the Lemures without him. In the beginning of the fifth season (''Sailor Moon Stars''), Hotaru [[PlotRelevantAgeUp rapidly grows back]] as her memories return, and the previous season's BigBad, Nehellenia, is returned to childhood to allow her to relive her life and avoid the mistakes that turned her into a villain in the first place.
** In the [[Manga/SailorMoon manga]], [=PallaPalla=] swaps Usagi and Chibiusa's in the first chapter of the Dream arc, which is actually done to depower the two of them. They eventually overcome it and transform into their proper bodies using their henshin phrases. Later in the same arc, Zirconia depowers both Sailor Moon and Tuxedo Mask in the same manner, turning them into six-year-olds and preventing them from accessing their magic. Pegasus reverses it by transporting them to Elysion, which has enough purifying power to break the spell.
* ''Manga/RosarioPlusVampire'' has an example of this one. [[TokenMiniMoe Yukari and Kokoa]], after realizing that they're not being taken seriously due to their age, use some of Yukari's age-up pills for a [[OvernightAgeUp temporary change]]. When the pills wear off, Kokoa finds herself ''younger'' than before. She finds herself in trouble shortly thereafter, only to be saved by the entire UnwantedHarem (sans Tsukune) turned into children along with her. Much cuteness and butt-kicking ensue.
* Episode 9 of ''Manga/SgtFrog'' features mother Aki Hinata getting turned into a teenager by Kururu's newest invention. In a later episode, the same gun turns Fuyuki into a kindergartner. Even later, Natsumi, Keroro, Giroro, and Kururu also get zapped by this gun. [[spoiler:In one episode, the entire planet gets zapped by this gun, setting time back by about twenty years.]]
* Happened in ''Manga/SketDance'':
** The first time was with Bossun after accidentally drinking Chuu-san's youth potion, mistaking it for a bottle of cola. Himeko [[CutenessProximity absolutely flips over him]].
** The second time was with Himeko and Momoka, several chapters later, at the same time, with the ''same bottle of cola''. Suffice to say, Bossun had a swell time looking after them.
** In the anime, two girls from the student council drink it on purpose, because "life is an adventure". Needless to say, it makes things even harder. In both versions, when the rejuvenated girls drink the antidote, they get ten years older than normal. And of course, by the time the next episode starts, [[UnexplainedRecovery they're back to their normal ages again]].
** Happened for the third time in Chapter 239, with [[TheRival Tsubaki]]. Except this time he reverted both in physical ''and'' mental state. Everyone, including Bossun and Daisy, gushes over [[CutenessProximity how cute he is]].
* Mosquito from ''Anime/SoulEater'' weaponizes this, being able to regress to any point in his extremely long life, which combined with his bizarre, chaotic life cycle gives him plenty of forms to change into, from a comically buff gorilla man to an elongated insectoid, to a humanoid vampire-esque figure, to an amorphous EldritchAbomination.
* In ''Anime/{{Stitch}}'', Babyfier (a creature that can turn people into babies) makes 3 appearances.
** In "Rivals stick Together" Babyfier is unleashed at a school turning most of the students and adults into babies.
** In another episode Babyfier turns the main character and her friends into toddlers.
** In the third episode, Babyfier is now good and turns a couple of the villains into babies.
* ''Manga/TheSevenDeadlySins'':
** The setting has a literal fountain of youth that makes the drinker immortal if they drink the entire fountain (which is just a cup). This is how Ban gained his immortality.
* Washu did this to herself in the ''Anime/TenchiMuyo'' OVA. [[spoiler:She was so distraught from her husband using his higher prestige to take away her child and leave her, she used her super-science to reverse her physical age to that of a 12-year-old so she'd never suffer that sort of heartbreak again. She can return at any time and explicitly says she'll do it if Tenchi'll have a child with her. Ryoko is not amused.]]
* Some chapters/episodes of ''Manga/ToLoveRu'' and the ''To-Love-Ru Darkness'' OVA feature a creature named the "skunk of youth", which regresses some of the main characters, among others, into kids.
** A trait of Lala's species is that if they exert too much energy, their bodies shrink to a younger state. This happens to her when she tries to stop Yami after being overtaken by her "Darkness" form, where she expends too much energy and shrinks to the size of a little girl.
* ''Manga/TheWorldGodOnlyKnows'':
** In the "Heart of Jupiter" arc, [[spoiler: Keima is sent back to the past via MentalTimeTravel and given a mission to save a cute but emotionless and mysterious young girl from committing suicide. If she gets overtaken by despair, she starts getting younger until she's transformed into a baby, which triggers a ResetButton that sends Keima back to the start of the mission. However, he can stop her from getting younger by kissing her before she turns into a baby]].
** The main manga also had a three-chapter spinoff called ''Magical Star Kanon 100%'', focused on, as the name implies, Kanon Nakagawa. In it, she is turned into a child by a Runaway Spirit and has to hide her identity and find a way to get back to her true age. The OVA version even has Elsie turn back into a child.
* In ''Manga/YuunaAndTheHauntedHotSprings'', the landlady's collection includes water from the Fountain of Youth that makes those who get splashed with it turn younger in body and mind. Nadare Tenko uses it in the "Yukemori Targeted Arc" to make everyone in the main cast younger.
* In the Dark Tournament arc of ''Manga/YuYuHakusho'', Ura Urashima uses a special mist meant to de-age its victims past the point of conception. Unfortunately for him, his target was Kurama, and once his human body went into non-existence, his previous incarnation - full-powered demon Yokokurama - manifested. Ura is so freaked out that it's Kurama rather than someone just using his name [[spoiler:his team captain]] has to [[https://www.youtube.com/watch?v=obfeTl5_S18 kill him]] to keep him from spilling all the beans.
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