* Subaru from ''Anime/DotHackSign'' is about the most likeable character in the show. Then in comes the ''GIFT'' AffectionateParody {{OVA}} where she poleaxes Ginkan for disregarding her orders so brutally that CensorSteam is employed in the scene (implying that it wouldn't be appropriate even for 17+ audiences).
* [[YamatoNadeshiko Belldandy]] from ''Manga/AhMyGoddess'' is a prime candidate, with her always presenting a quiet and gentle personality. Because she has such incredible self-control and such a kind personality, she's given access to more power than anyone else in the series, with the exception of Hild (and the Almighty, but he doesn't appear).
** When her self control slips, nearby glass shatters and pipes burst. Seeing a pattern, Urd exploits Belldandy's jealousy, which makes Belldandy subconsciously create an explosion so powerful it defeats Garm, who outclassed Urd.
** When they're at the hot springs with the demon Mara, Belldandy lays down a rule against fighting. "And if you break it, I will punish you." Urd and Mara are understandably unnerved.
** And ''God save your soul'' if you [[BerserkButton dare to hurt Keiichi]]. She's scary enough when she's just disappointed in your actions... this will flat-out make her ''angry''. The first time this happens in the manga, she does not hesitate to unleash her "Holy Wind Press", an ''attack'' spell, on his assailants ([[spoiler:a brainwashed Tamiya and Otaki]]), a sight which absolutely ''terrifies'' Skuld.
** She [[spoiler: is shown to be an excellent fighter who has a Valkyrie license. She just doesn't like to fight]].
** Seriously, Bell-chan is a rather bossy girl by nature. Her sisters are even a little afraid of her. She is just really, REALLY good at covering it up with her gentle facade. If she wanted, she could make Keiichi do [[{{MoreThanMindControl}} absolutely anything]]. Thank the almighty she's the nicest person you will ever meet.
** Speaking of Valkyries, Lind is [[SilkHidingSteel a polite and proper girl with the kind of decorum you would expect of an]] OfficerAndAGentleman. Her job description? Heaven's Own OneManArmy.
* Hanji Zoe from ''Manga/AttackOnTitan'' comes across as extremely cheerful and eccentric, being one of the most friendly senior officers in the Survey Corps. Though something of a NightmareFetishist when it comes to Titans, it really is easy to forget that Hanji is a veteran soldier in the branch with the highest mortality rate and ''not'' someone to make angry. Though slow to anger, Hanji shows no mercy once provoked -- dangling a priest 50 meters off the ground to interrogate him and on another occasion, calmly preparing to engage in a bit of ColdBloodedTorture against a captured enemy.
** Armin Arlert may be physically the weakest among the trainees and since childhood constantly depended upon [[LittleMissBadass Mikasa]] and [[HotBlooded Eren]] to protect him, but he's also a tactical genius who can quickly deduce his enemies' weaknesses and has no qualms about exploiting them. His taunt to [[spoiler: Bertholt]] about how [[spoiler: Annie]] [[KickTheDog was being tortured]] to make him lose focus was both genius and disturbing.
* In ''Webcomic/AxisPowersHetalia'', Hungary, the cute young girl who was Austria's maid and later advisor before marrying him, will not hesitate to invoke her [[NinjaMaid massive fighting skills]] (which she acquired [[CuteBruiser when she was a pint-sized warrior girl]]) and maul you if you hurt her husband (Well, [[YaoiFangirl she might hesitate if you're a cute male and you're molesting him]]. And not ''always'', mind you. You're warned, France)
** And Lithuania? That nice guy? Quite a good spy and fighter who won't hesitate to put a knife to your neck if your threaten someone he cares for, specially his old friend Poland. You're warned, Prussia.
*** As a rule, ''everyone'' in the Baltic/Soviet region is a case of BewareTheNiceOnes. Even the ShrinkingViolet little brother of Lithuania, Latvia... Having a PsychopathicManchild as your boss leaves marks on you, indeed.
** As a child, [[spoiler: Italy]] at one point completely kicked Turkey's ass. Turkey's 'I really hate kids' says it all. [[http://i40.tinypic.com/29ol451.png Greece is amused.]]
** Let's not forget that, if you make the sweet {{Meganekko}} [[RomanticRunnerUp Canada]] lose his patience, you'll find yourself on the receiving end of a hilarious yet absolutely ''epic'' TheReasonYouSuckSpeech. If America couldn't get his brother off his back for ''three'' hours straight, then so won't you.
** Remember Finland? Finland? Sweden's "w'f"? Finland with the adorably off naming skills and the food preferences of a pregnant rat on acid? Well, while it's not shown in the strips just yet, plenty of fanfic has explored [[http://en.wikipedia.org/wiki/Winter_War why it's probably best not to forget.]]
*** His partner Sweden is a GentleGiant of few words who dotes on his "w'f", but in the aftermath of the April Fools' Day, [[http://aph.starry-sky.com/42_1.html it's him who thinks of the punishment for France.]]
** Ukraine is a sweet TeamMom and FragileFlower... who will subtly manipulate her ''[[{{Yandere}} very scary]]'' younger siblings to get what she wants from them and [[PluckyGirl will hold her ground if she has to.]]
** [[CoolBigSis Belgium]] is shown to be a rather [[NiceGuy Nice Girl]] prone to HeroicSelfDeprecation, but her profile refers to her as being scary when she's mad. The fact that she has a [[{{BFG}} rifle]] and [[ActionGirl looks like she knows how to use it]] indicate that this probably would not be a good thing.
* Jonathan Joestar, the protagonist of the first story arc of ''Manga/JoJosBizarreAdventure'', is a kind and mild-mannered gentleman. Nonetheless, he is not above fighting when his friends and family are in danger, not to mention the time he flew into a blind rage when he realized Dio Brando ruined his budding relationship with Erina and gave him a NoHoldsBarredBeatdown.
* ''LightNovel/{{Baccano}}'' seems to like this trope a lot. Many of the characters come across as very amiable individuals--that is, until you push them too far. For example: [[spoiler:The resident ShrinkingViolet Jacuzzi Splot once shot up eighteen Mafia speakeasies single-handedly, in one day, on a RoaringRampageOfRevenge after the Russo Family kills several of his friends]].
** [[spoiler: Claire Stanfield]] wasn't planning to kill you--no, siree. All he wanted to do was conduct his train, ogle that cute girl in the first class car, and tell silly ghost stories to pass the time. But no, you just ''had'' bring this whole "train hijacking" thing into this. And [[{{Retirony}} Tony]]--did you ''really'' have to kill Tony? What did he ever do to you? Oh well, it's too late now. He's just gonna have to [[TortureTechnician teach you a lesson]] now. [[AxCrazy A very painful, bloody lesson]]...
** In the {{Light Novels}}, Eve Genoard also enacts this trope. When [[spoiler:Gustavo Baggeta]] brags to her that he killed her father and oldest brother, she almost immediately casts aside her status as TheIngenue, picks up a dropped revolver, and tries to blow his head off.
*** She shows signs of this in the anime as well, when she escapes from the Runoratas by tying one of them up, and possibly knocking him out as well.
*** The anime example doesn't really count, as the "Runorata" who was tied up was actually a spy and a good guy, and it's heavily implied (really all but outright stated) that he let her go and tied himself up.
* Yoshitoki in ''Manga/BattleRoyale'', is normally shy and mild-mannered! When Kinpatsu Sakamochi/Yonemi Kamon depending on which media type you read kills [[spoiler: the woman he loves, Miss Ryoko]] he goes beserk and runs at a armed man. [[spoiler: It didn't end too well.]]
* Leo Aoi of ''Beast Master''. Despite his scary face, he's as sweet as a guy can be, but when he sees blood, or God forbid, you try to hurt Yuiko, he will kill you if Yuiko doesn't stop him in time.
* [[spoiler:Grell Sutcliff]] from ''Manga/BlackButler''. Through most of the Jack the Ripper arc, he's the quiet/suicidal/klutzy butler of [[spoiler:Madame Red]] who more or less functions as comic relief [[RunningGag through his epic failure at his work.]] Until you catch him, of course. Then he pulls a grin that can be nightmare-inducing at best, proceeds to change his appearance dramatically and turns into a chainsaw-wielding psychopath that is very forward about his creepy attraction to Sebastian, ''within the same five minutes'' talking about both wanting to cut him into pieces and bearing his child. [[spoiler:It's revealed that he's a shinigami gone pseudo-rogue and has been half of Jack the Ripper, allowing Madame Red to commit her crimes without being noticed. The useless butler routine was just to keep suspicion off him.]] He helps [[spoiler:Madame Red]] kill the prostitutes because it's a distraction and he's bored with sticking to his list; [[spoiler: it's also speculated that, as an okama, Grell shares Madame Red's frustrations about being unable to give birth]].
** Then there are the [[spoiler:servants of the Phantomhive family]], klutzy, bumbling, carefree, and happy. Then the circus comes to town and we learn why they have the jobs they do.
*** Especially [[spoiler:Finnian]] in the manga, the last person you would expect to preform a cold grizzly murder of a man while his friends watch in horror.
* In ''Manga/BlackLagoon'', Rock is by far the nicest person you will find... but if you push him TOO far, [[spoiler: particularly by wantonly abusing an innocent girl he was trying to help,]] he will show you that he ''is'' just as dangerous as his crewmates. [[spoiler: This is after all the guy who took out an airborne helicopter with a torpedo. And flicked off the helicopter as it exploded.]]
** [[SilkHidingSteel And the female employees of the Lovelace Family are also not to be trifled with, despite their demure and deferential exteriors]]. ESPECIALLY Roberta. Lay a finger on the Young Master and she will kill you. [[spoiler: Repeatedly. With a .50 caliber sniper rifle, ONE-HANDED.]]
* ''Manga/{{Bleach}}'':
** Captain Retsu Unohana. A [[TeamMom motherly]] YamatoNadeshiko type in charge of a company full of healers, one look from her can scare anyone. Even people who don't scare easily such as Kenpachi Zaraki. [[spoiler:She is the First Kenpachi and creator of the [[BloodKnight 11th Division]]. She named herself "Yachiru" to reflect the fact she's a MasterSwordsman and was the most diabolical criminal in Soul Society history before she became TheAtoner.]]
** GentleGiant Hachigen Ushoda manages to stay calm and polite even when he reveals himself to be ''pure BadAss''.
** Handsome GentleGiant Chad who refuses to harm even bullies, but don't '''ever''' threaten his friends.
* The Hakuho Academy Space Yacht Club from ''LightNovel/BodaciousSpacePirates''. Do not confuse them for a bunch of easily-scared high school girls if you value your retinas.
* ''Manga/CardCaptorSakura'': Sakura is cheerful and caring, but the Snow Card will forever remember what happens if she gets REALLY angry... During the fight Sakura loses the wristwatch Yukito gave her as a birthday present, and since she had a crush on him this triggers her BerserkButton. OneHitKill with the Fire Card. Shaoran got ''really'' scared at that.
* [[{{Change 123}} Motoko Gettou]] is a ''double'' instance. If you mess with her, you get beaten up by one of her [[SplitPersonality split personalities]], of which there are three; each with its own individual conscience and each as badass as the next. Assuming you somehow manage to beat ''those'', enjoy it while it lasts; [[spoiler:[[SuperpoweredEvilSide you'll be dead in a moment.]]]]
* Chrono of ''Manga/ChronoCrusade'' is a AdorablyPrecociousChild that often gives speeches about ThePowerOfFriendship and behaves politely even to people that don't trust him because he's a demon. But he ''is'' a demon, and when his powers are unsealed he turns into his true form--a bishounen powerhouse [[DepartmentOfRedundancyDepartment with massive amounts of power]]. When his BerserkButton is pushed, he's been known to fly into UnstoppableRage fits with little thought to any collateral damage that may occur.
* ''Anime/CodeGeass''[='=]s Princess Euphemia doesn't count [[spoiler: since her genocidal rampage was caused by Geass and not any of her own pent-up aggression]], but [[ShrinkingViolet shy little]] {{fangirl}} [[{{Meganekko}} Nina Einstein]] certainly does. She's almost perfectly normal, aside from her deep-seated fear of Japanese people and her [[SchoolgirlLesbians rather obvious crush on Princess Euphemia]], who intervened to [[RescueRomance save her from Japanese terrorists]]. [[spoiler: When Euphinator was killed by Zero]], though, she promptly turns a previous offhand mention of her technical skill in a prior episode into [[spoiler:building a hybrid nuclear/sakuradite bomb that causes an instant stalemate between Britannia and the Black Knights, as it's theoretically powerful enough to destroy all of the Tokyo Settlement if she triggers it, which the emotionally distraught girl is perfectly willing to do just for a chance to kill Zero]].
** A running gag among certain circles is that the sweetest, most innocent character, Nunnally Lamperouge, actually hides a [[http://i65.photobucket.com/albums/h201/jin0014/Code%20Geass/code1_tomatopoza.jpg horrible dark side]] that will surface if she ever gets a Geass of her own or indeed regains sight.
*** Considering what happens in the ''Nightmare of Nunnally'' AlternateUniverse manga [[spoiler: and what happened in Episode 22 of R2]], the possibility ''is'' out there.
** Suzaku definitely counts, though. He's an all-around NiceGuy who just wants peace, but will destroy pretty much anyone who threatens to upset the current peace. After the Euphemia example above, it just gets worse, since he outright ''stops'' being nice.
*** Suzaku is a bit of a deconstruction because he was HotBlooded in his childhood to begin with. As pleasant as he can be in the present, his current drive for peace, though, is just part of a [[spoiler:[[DeathSeeker death wish]] from killing his father seven years earlier]]. Once the Euphemia example happens as mentioned, it's little surprise that his old bitter headstrong habits resurface.
** Lelouch is a questionable one. He WAS a NiceGuy, but then his mother died, his sister was maimed, and his family abandoned him. By the time he walks through a village of shredded bodies, "nice" is just a mask he remembers how to wear.
*** He still does have a degree of kindness that roots itself in his desire to change the world, but there's no question that this series involves a great deal of his own catharsis. Even so, you can't deny he still did manage to show how much he was really holding back once he passes the DespairEventHorizon.
* ''Manga/DanceInTheVampireBund'': Do not mess with [[spoiler: the fangless--vampires who willingly pulled out their fangs to preserve their humanity--because having the weaknesses of/being hated by both vampires and humans made them ''the best guerrilla fighting force on the planet''. For example, when a powerful vampire clan raided the Bund and started rounding them up, the fangless responded by leading the main force into a tight hallway filled with RazorFloss and ''dropping their entire apartment complex'' on the rest]].
* In ''{{Dangaioh}}'', an ex OrdinaryHighSchoolStudent is TheLeader of the group that pilots the huge SuperRobot that gives its name to the series. Why? Because Miya Alice is capable of unleashing ENORMOUS PsychicPowers once she's mad, frightened, or determined to fight and protect her partners: [[FragileSpeedster Roll]], [[BrokenBird Pai]] and [[ExtraordinarilyEmpoweredGirl Lamda]].
* In the last episode of ''Manga/DeathNote'', TheDitz character Matsuda, [[spoiler:upon learning that Light is actually Kira, breaks emotionally and shoots Light's hand when he tries to use a piece of the Death Note. When Light tries again, Matsuda flies into a furious rage and then seriously wounds Light with a barrage of bullets, only prevented from delivering the CoupDeGrace by the other officers]].
-->'''Matsuda:''' [[spoiler:"I'll kill him! I'LL KILL HIM! '''HE HAS TO DIE!'''"]]
* Toyed with in ''Manga/DetectiveConan'' with Okiya Subaru, a friendly Sherlock Holmes-loving grad student living in Conan/Shinichi's house [[spoiler:who also gives Haibara/Sherry the chills, which only happens around Black Organization members. Most likely it's just a "friends close, enemies closer" plan]].
** Conan's excuse for letting the fox-faced Subaru stay at his house: "A person who loves Sherlock Holmes ''couldn't possibly'' be evil!"
** Don't forget Ran Mouri, either. A beautiful girl with nice legs and a motherly disposition, okay? Well, either [[ClingyJealousGirl tell her you may have a shot at Shinichi's heart]] or [[MamaBear threaten Kogoro, Conan, or anyone she cares for]]. [[ActionGirl Ran will show you no mercy]].
* ''Manga/DGrayMan'': Allen Walker is a cheerful, kind young man [[AllLovingHero who loves everyone]], and has made it his mission to not only save humanity, but also release akuma-captured souls from their pain and suffering. But do NOT get him angry, because he will make the offender very, VERY sorry.
** General Tiedoll is probably an even straighter example. He has one of the most ridiculously [[SuperpowerLottery powerful]] Innonences so far (being able to manipulate nature, including making mile-high white wooden {{Humongous Mecha}}s and creating a city-sized anti-akuma blast without actually harming the city), is a skilled artist and treats younger Exorcists like sons (to the point where he teared up when he thought Kanda wasn't gonna return from the Ark in time). We have yet to actually see him angry, which makes the above mentioned feats even scarier.
* In ''Anime/DigimonAdventure'', Gabumon is probably the gentlest and sweetest-natured of the original 7 Digimon partners. However, pose even the remotest threat to Matt ([[UpToEleven even if you ARE Matt]]) and he will show you just how dangerous a wolf he can be. Case in point: Remember when I said "even if you're Matt"? Well, when Matt [[HeroicBSOD started sinking into depression late in the show]], Gabumon took it upon himself to pull him out of it...[[GetAHoldOfYourselfMan by BITING the kid]]!
* In ''Anime/{{Digimon Adventure 02}}'', Takeru/T.K. is normally a nice guy, unless you happen to be meddling in the [[BerserkButton powers of darkness]], or trying (and failing) to [[CrowningMomentOfAwesome whip him senseless]], leading to a MegatonPunch in return.
** Hikari/Kari doesn't tend to get angry, but ''do not'' kill her friends. Vamdemon/Myotismon and Mugendramon/Machinedramon both made this mistake. In both cases, it was the last mistake they would ever make. [[spoiler:Subverted, though, in that both of them barely survived and later returned in OneWingedAngel forms, which returned yet again after they were defeated the second time.]]
* In ''Anime/DigimonTamers'', Takato is the least HotBlooded out of all the goggle boys of the series. Guilmon was this by default ([[LetsGetDangerous naïve, yet a powerful fighter]], [[PigeonholedVoiceActor voiced by Masako Nozawa]]--[[DragonballZ remind you of anyone on this page?]]), but Takato [[UnstoppableRage snaps]] when [[spoiler:Beelzemon kills Leomon permanently]]...he was already [[HellishPupils not willing to forgive]] [[spoiler:Beelzemon]] right before that moment, [[DeadlyUpgrade but what happens next]] is reminiscent of ''[[Anime/DigimonAdventure Adventure]]''. [[spoiler: Takato made [=WarGrowlmon=] turn into his 'natural' final stage - the EMBODIMENT OF APOCALYPSE ITSELF, an abomination whose mere existence was a hazard to the integrity of both worlds, ''through sheer anger alone''. He then sent it to EAT his opponent.]]
* Gohan in most of ''Manga/DragonBall Z'' is a pacifist who abhors violence, but when provoked (namely by hurting his precious people, or just any InnocentBystander for that matter), can fly into a [[UnstoppableRage near psychotic rage]] and suddenly increase his strength to colossal heights. Through this he was the first to unleash the devastating power of a Super Saiyan 2, which also turned him from the kindhearted boy he is into a [[SuperpoweredEvilSide sadistic homicidal monster]] with the power to decimate ''entire Solar Systems!''
** Goku, even when fighting seriously to avenge fallen comrades or save the world, maintains a constant sunny disposition and childlike naïveté throughout the series, allowing for humor in otherwise climactic battles. Goku only completely snaps when Frieza mercilessly kills his lifelong friend Kuririn. His first transformation into a Super Saiyan turns him into a cold, taunting, ruthless and arrogant fighter who starts to beat Frieza to within an inch of his life. It wasn't the first time either -- when Kuririn is murdered by one of Piccolo's minions, Goku takes off in a blind rage swearing bloody revenge.
** Future Trunks would fit this trope well. He's normally a quiet and polite guy, but growing up in a BadFuture turned him into the most merciless of all of the Z fighters. He won't even think twice about slicing his enemies and turning them into dust. Heck, for the sake of preventing the nightmare from happening twice, he wouldn't hesitate to blast anyone. His own father, Vegeta, found this out the hard way.
* In ''LightNovel/{{Durarara}}'', the nicer you are, the more the character is messed up in the mind. [[spoiler: [[CrouchingMoronHiddenBadass Mikado]] is the pure definition of this trope as he can switch from being the nicest person in the series to the scariest when he's angered. [[TranquilFury And when he's angry, he means everything he says]]]].
** Shizuo Heiwajima is a quiet yet somewhat shy and awkward young man who hates violence. He's also [[SuperStrength Shizuo]] [[HairTriggerTemper Heiwajima]].
* Nyuu from ''Manga/ElfenLied'' is a cheerful, super cute blank slate girl, but try to hurt her and she will become Lucy, her deadly and stone-cold counterpart. Instant YourHeadASplode!
** Lucy's first major massacre was a textbook example of a BewareTheNiceOnes snap-out: [[spoiler:As a child, she lived at an orphanage where [[KidsAreCruel the other kids were absolutely cruel]], tormenting and harassing her for her "cute little horns" and [[EmotionlessGirl emotionless nature]]. They finally pushed Lucy too far when she started caring for a puppy and they [[MoralEventHorizon forced her to watch as they kicked it around and beat it to death with a vase, just to get her to show]] ''[[MoralEventHorizon something]]''. Lucy unleashed her diclonius powers for the first time, leaving no witnesses]].
* GentleGiant Kurita in ''Manga/{{Eyeshield 21}}'' is probably the nicest, friendliest character in the entire series. He is also the main linesman of the Deimon Devilbats and he will ''crush you'' to protect his team. In fact, his strength ''increases'' the more people he has to protect.
* ''Manga/FairyTail'': Mirajane is usually calm, friendly and a non-action member of the guild. But if you have anything to do with someone she cares about facing potential danger, this trope starts to manifest in her "demon" glare. And when someone nearly kills her younger brother, she activates her Satan Soul transformation and savagely tramples her opponent. Just about everybody in the entire guild has at least shades of this trope, but it's most pronounced in Mirajane because she's ordinarily extremely sweet and kind to everyone she meets.
** Oddly enough, [[spoiler:[[BigGood Mavis]]]] qualifies. Friendly, sweet, and NotSoAboveItAll in regards to the guild... but then she comes face to face with [[spoiler:[[BigBad Zeref]]]], someone she apparently has a history with, and responds to his threat of being an OmnicidalManiac with '''''a flat-out death threat''''', something that is otherwise [[ThouShaltNotKill a big no-no]] in Fairy Tail, as well as legal guilds in general.
* Chiffon Fairchild of ''Manga/{{Freezing}}''. One of the very few [[OnlySaneMan sane]] [[ReasonableAuthorityFigure people]] among a student body of {{blood knight}}s, she ''is'' still ranked number one in school... and known as "Unmatched Smiling Monster". Uh...
* ''Literature/FromTheNewWorld'': Asahina Tomiko, chair of the "ethics committee," and the only member who treats Saki and her friends with anything approaching respect. She helps them out of several tricky situations, and always seems polite, reasonable, and levelheaded. But when [[spoiler:Yakomaru's army invades the village during a festival, killing many people, including one of her friends,]] she does not plan on taking it lightly.
-->'''Tomiko:''' "We must punish that horrible monster rat [[spoiler:Yakomaru]]. I promise you...[[NeverMessWithGranny I will kill him slowly, and he will die in more pain than any creature has ever suffered."]]
* ''Manga/FruitsBasket'' has at least two examples, if not more. Kagura Sohma is usually a cute, sweet girl with a cheerful disposition, but she actually shows her love for Kyo by beating him to a pulp on sight, especially if he refuses her advances. This frequently leads to Shigure's house being broken. When they were both little kids, apparently she got Kyo to propose to her by threatening him with a knife (or a big rock in the anime). Hatsuharu Sohma is usually kind, if eccentric and a little out of it, but when he snaps he turns into "Black Haru", a bloodthirsty version of himself with a whole lot of attitude. Both are not to be trifled with, and whatever you do, do NOT touch their love interests.
* ''Manga/FullmetalAlchemist''
** For the most part, Major Alex-Louis Armstrong is a LargeHam GentleGiant. Emotionally scarred by the idea of killing civilians, always trying to give his opponents the chance of surrendering, had a ''terrible'' HeroicBSOD during the Massacre of Ishbal, etc... Then a homunculus goes and tries to kill his older sister, and so he kills it until it dies.
** Alphonse is a GentleGiant who wouldn't hurt a fly, but he has come close to flying into a merciless rage (and does a few times in [[Anime/FullmetalAlchemist the first anime]]) on multiple occasions. You do '''not''' want to mess with those he cares about. Seriously, DON'T. If his older brother Ed can't beat him in a fight, you won't.
* In ''FullMetalPanicFumoffu'', there is a janitor who is known to be very kind to anyone. He stays gentle when Sousuke and the Karate club leader destroy a big part of the school attempting to help, but when they serve him a dish, a fish named Catherine whom he considered a daughter, he attempts to kill them with a chainsaw, and proves to be NighInvulnerable, by being shot many times with a shotgun and some grenades without any ill effects.
* ''GalaxyFrauleinYuna'''s title character: [[GenkiGirl sweet, bubbly]], loves making friends [[AllLovingHero with everyone she meets]], whether they [[DefeatMeansFriendship started out hostile]] or not. If you value your continued existence, ''absolutely do not [[UnstoppableRage kill any of her friends]]''. Beating them up but letting them survive is apparently okay, but Genmu [[BerserkButton crossed the line]] and paid for it.
* Rushuna of ''{{Grenadier}}'' is a sweet MsFanservice whose goal is to get people to stop fighting by the power of her smile. When that doesn't work, she pulls out her six-shooter and [[ImprobableAimingSkills blasts anything that moves.]] A castle full of riflemen led by an armored giant wielding a machine gun, who won't release the helpless prisoner?
--> '''Rushuna:''' "You don't get a smile!" ''(she proceeds to shoot EVERYONE)''
* Henrietta in ''Manga/GunslingerGirl'' is as cute as a button... until an assault on her beloved handler Giuseppe brings back subconscious memories of her own childhood trauma. Then she proceeds to kill everyone in sight.
** Actually, the organization that Henrietta is a part of is basically built on this trope, with a small battalion of cute, dormant psychopaths, including one who continually keeps a LimitBreak saved up until she ends up being kidnapped in place of the bad guys' actual target. Yeah... that didn't go so well.
* Kamijou Maki from ''HayateCrossBlade'' is perhaps the most notable example in her series. For almost 6 volumes, the readers hardly ever see her making an appearance for more than a couple of pages (which was even lampshaded in a side story), and when they do, she's portrayed as a whipped, mild-mannered, low-profile dork. [[IAmNotLeftHanded Then one opponent breaks her right arm]]. Her response? [[LetsGetDangerous "The judges can't stop me here. How lucky."]]
* ''Manga/HayateTheCombatButler'''s titular character, who does this in both the anime and the manga whenever Nagi gets kidnapped. First during the first episode's car chase and more comically when he takes down a giant mecha with an ''machine gun.''
** Maria certainly qualifies, arguably in a greater extent. Just say something about [[BerserkButton her age.]]
*** The ''narrator'' is afraid of her! Let us clarify: The narrator, which is voiced by Creator/NorioWakamoto, is scared of her. Let that sink in for a minute....
* Seras Victoria from ''Manga/{{Hellsing}}'' seems to start off as a sort of as a [[WideEyedIdealist Wide-Eyed Idealist]] until the Valentines' attack on the Hellsing base sends her into an UnstoppableRage which you might think hails from her vampiric nature, culminating in [[spoiler:grinding Zorin's head along the wall until her face is obliterated and her skull shatters]]. However, a detailed look into Seras "Kitten" Victoria's history reveals she's had a vicious temper as far back as her childhood in an orphanage when she brutalized a fellow orphan who was bullying and tormenting her, and that she's been actively keeping that violent part of herself in check since ''long before'' becoming a vampire.
* In ''VisualNovel/HigurashiNoNakuKoroNi'', Rika herself notes, regarding the main cast, that, "They are all caring, gentle individuals. And yet, [[spoiler: once the wheels of fate go awry]], they become controlled by delusion and start committing deadly acts of violence." Considering how much this anime seems to enjoy [[BreakTheCutie breaking cuties]], this shouldn't come as a surprise.
** In the end however, the ''BigBad'' plotting all the terrible occurrences turns out to be an apparent Nice One as well, [[spoiler:even if she (Miyo Takano) looks half-stoned at all times, moonlights as a [[HelloNurse nurse]], and apparently dies early into every cycle]].
** More so. [[spoiler: Her StartOfDarkness shown in last arc, reveals that Takano is in fact a [[BreakTheCutie broken cutie]]. While she was a nice young child... having her parents die and then getting sent off to a particularly monstrous OrphanageOfFear leads her to angrily defy god.]]
* ''{{Hitohira}}'': Beware of Nono when she's angry.
* Gon from ''Manga/HunterXHunter''. Cute, lovable, Gon... don't hurt or threaten any of his TrueCompanions. Seriously, don't. He's scarier than Killua when pissed.
* Played completely straight near the end of ''{{Inukami}}''. The local YamatoNadeshiko (appropriately named Nadeshiko) finally snaps when the BigBad of the series [[spoiler:kills her "master" and love interest, Kaoru, after leading him in an EvilPlan designed solely to cause Kaoru to suffer despair.]] Nadeshiko prays to the Heavens for a power [[spoiler:that she gave up because of nearly killing an entire human village after losing herself in bloodlust]] and proceeds to wail on the BiggerBad for some time.
* Plutia from ''HyperdimensionNeptuniaVictory'' is a quiet, ditzy and pretty lazy young lady... but when she gets mad, she transforms into a [[TheBaroness sadistic]] {{Dominatrix}} with a spiked and electrified whip who scares even the {{Big Bad}}s with her ability to dish out pain and effectively MindRape people.
* Rika from ''Manga/KareKano'' for most part is a quiet, unassuming girl but when she was a kindergartener, Rika found out that Kyo, an older boy who usually looks after her, was getting picked on, she saved Kyo from the high school bully by [[spoiler: bashing him with a baseball bat. She really must have done a number on the guy, as she had blood splatter over her face]].
* Nanami of ''LightNovel/{{Katanagatari}}'' gives us the impression of just being Shichika's demure, [[IllGirl sickly]] older sister. Then comes Episode 4 and the Maniwa Insect Squad with the intent of capturing or killing her, and it turns into a [[CurbStompBattle one-sided slaughter]]. She even gives off a SlasherSmile while she's at it.
** It's also worth mentioning that at this point of the story she seems to be [[spoiler:the strongest character in the series, who's not only immune to non-lethal poisons and generally unable to die, but also able to learn most techniques by seeing them once and master them after seeing or using them a '''second time''' (not to mention that she's probably ridiculously strong, since she was able to easily fight with the main character knowing same techniques as him)]]. You should never underestimate nice characters...
* When it comes down to it, [[CrouchingMoronHiddenBadass Yamamoto Takeshi]] from ''Manga/KatekyoHitmanReborn'' definitely fits this. Put a [[SeriousBusiness baseball]] in his hands, or tell him to throw or hit something, expect him to get a serious samurai look and go absolutely all out on a simple game or task. Ask a poor, injured [[ButtMonkey Lambo]] who just wanted to play catch. Though... [[http://www.youtube.com/watch?v=E1tcAAMmCE8 this comes in handy sometimes]]. And don't forget Tsuna, at some moments. Especially when Genkishi decided to say he left Tsuna's friends for dead. [[http://manga.animea.net/kateikyoushi-hitman-reborn--chapter-213-page-6.html Here comes the berserker rage]]. And [[spoiler: poor Yamamoto, the usual happy man, was nearly chopped into two, possibly paralyzing him]]. And Tsuna, who was planning to [[spoiler: step down from the position of Vongola Boss]], doesn't do that, but willingly accepts it, with a pained look in his eyes as Yamamoto's attackers [[spoiler: the Simon Family, were right beside him]]. Whether that new family has gone past MoralEventHorizon, to hurt the Vongola, specifically, Yamamoto, [[http://manga.animea.net/kateikyoushi-hitman-reborn--chapter-294-page-17.html Tsuna's still very... very upset]]. It's not normal for Tsuna to lash out, though, obviously.
* Miu in ''Manga/KenichiTheMightiestDisciple''. Normally she's very amiable and rather pacific, but if you [[spoiler:put all her friends on the verge of death? She ''snaps'' and can no longer recognize friend from foe and will kill anyone who gets in her way. Not that she actually managed to before Kenichi stopped her.]] Miu mentions offhandedly that one of the reasons her grandfather travelled with her as a child was probably to get her immense rage under control. [[spoiler:Possibly runs in the family, judging by her father.]]
* Fuyuki from ''Manga/KeroroGunsou'' is normally an ExtremeDoormat. Push him far enough, though, and everyone including Natsumi becomes scared of him. His expression is deliberately not shown during these times, but it's implied he looks a bit like a berserk [[Anime/NeonGenesisEvangelion EVA]].
** Tamama and Momoka, too.
** Dororo is perfectly content to lounge around all day, drinking tea, and enjoying nature. But when the chips are down, he isn't afraid to demonstrate the skills that made him a top assassain back home.
* Kimba from ''Manga/KimbaTheWhiteLion'' is a sweet and caring lion cub who is willing to help out those in need, a diplomatical and peaceful leader who tries to avoid fighting, and is more than happy to forgive those who want to reform themselves... But he also has super strength and vitality, the ability to summon many powerful creatures, which ranges from boulder-carrying hawks, and powerful chimps that fight along side him, and he puts all of that to good use in the battlefield; just look at all of the hunters, rhinos, hyenas, and other big cats he defeated.
* Koharu of ''KoharuNoHibi'', [[StalkerWithACrush defin]][[{{Yandere}} itely]].
* Of the two women central to the {{Leijiverse}}, [[Anime/CaptainHarlock Emeraldas]] is a merciless pirate and [[spoiler:her sister]] [[GalaxyExpress999 Maetel]] is generally described as the Nice One: gentle, kind, a bit mysterious. The latter also blew up a planet because a mad doctor tried to steal her body.
* After getting forced to play the sycophantic second fiddle to [[{{Yandere}} Akira Kogami]] for 19 episodes only to get sent out to hike up Mount Fuji for three weeks, lose his spot to a dumb [[Creator/DaisukeOno bishounen]], and get yelled at by Akira because the water he brought back was warm, [[EnsembleDarkHorse Minoru Shiraishi]] of ''Anime/LuckyStar'''s ShowWithinAShow finally lets Akira and her new assistant have it and trashes the set.
** He's even drawn slightly differently after the event, changing from his [[EyesAlwaysShut permanent closed eyes]] to tiny, pissed off ones. Even when he's ''not'' pissed off.
** Ayano, a NiceGirl with the tendency to be TheNonDescript, also has one of the series' most angry [[BlueWithShock Blue With Anger]] moments.
* [[NinjaMaid Elenore]] [[PluckyGirl Baker]] from ''Anime/{{Madlax}}''. Go ahead and touch her mistress, Margaret...Just ask Maurice Lopez.
* ''Manga/MagicKnightRayearth''. [[PluckyGirl Shidou Hikaru]] is a bubbly, animal-loving, always ready-to-help fourteen year old girl but ''don't'' hurt her precious Umi and Fuu or she might end up wiping the floor with you. [[spoiler:Her anger gives her such strength that she manages to make a considerable magic upgrade ''almost immediately after receiving her powers'' just because someone injured Umi!]]
* Hayate Yagami from ''Anime/MagicalGirlLyricalNanoha'', who is the master of a [[TomeOfEldritchLore dangerous book]] that her guardians want to complete, as well as a sweet and caring girl that wouldn't hurt anyone. You can see where this is going. It does take a massive gambit to both give her the power to do this and a reason to snap, but snap she does.
** Then we have Nanoha herself, whose sweet and innocent persona distracts from the fact that she has the power of a PhysicalGod. Her favorite method of making friends seems to be [[DefeatMeansFriendship beating them to near death]] and [[WarriorTherapist asking questions while she does it]]. And heaven help you if she actually gets ''angry''. The oft-cited example of her blasting Teana to unconsciousness during a training battle ("Shall I... cool your head a little?") doesn't even come close to receiving her ''real'' wrath, which involves being on the receiving end of a WaveMotionGun. [[DungeonBypass From across a battleship, if she has to]].
** And the ''[[ChurchMilitant battle nuns]]'' of the Saint Church, who can go from caring nurse to hard-boiled soldier in a matter of seconds.
** Most of Riot Force 6's combatants are generally nice people that have combat capability equal with (at least) heavy artillery. And they can be really, really scary when they [[UnstoppableRage snap out]].
*** Especially Caro Lu Rushe. A gentle, big eyed, shy little girl, a [[RankInflation B Class mage]] [[TheMedic specialising in buff spells,]] what could she possibly do? Piss her off enough [[spoiler:[[BerserkButton by destroying her home]]]] so she actually taps into her summoning magic and run for your Super Robot, because whatever she summons [[PhysicalGod would be more than appropriate to fight it.]] That said, your Super Robot needs to be LARGE to even stand a chance...
*** Subaru Nakajima is known as "Gaogaigar-tan" for the enormous number of shout outs in her combat style, [[spoiler:and the fact that she's ''literally'' a cyborg who resembles a young girl but was built for all-out physical combat ([[RousseauWasRight not that her origins matter much]] in ''that'' setting)]]. Her berserker moment brought upon [[spoiler: her older sister Ginga being beaten near death and kidnapped by the Numbers]]. [[strike:would be a CrowningMomentOfAwesome if it weren't so damn terrifying]] is [[Awesome/MagicalGirlLyricalNanohaStrikerS SO SCARY IT'S AWESOME]]. "Give...''her''...'''''BACK'''''!"
** Similar to Bleach's Unohana, [[TheMedic Shamal]] is typically kind, polite and soft-spoken, but when she gets angry, even Nanoha is scared of her. This could be because the first time Nanoha encountered Shamal, she managed to use teleportation magic to steal Nanoha's Linker Core from afar, rendering her unconscious.
*** Lets put this in perspective. She literally reached into Nanoha from a mile away, and effectively ripped out the core of her magic. And the scary part is, when they do that, there doesn't seem to be any counter to it.
** Touma from the ''Force'' manga also qualifies He's shown himself to be dangerous, but not in control of the power of his Divider through most of the manga, but when the TSAB forces attack the Huckbein airship, resulting in a massive melee between the bloodthirsty Huckbein and the reconstituted Riot Force 6. The resulting carnage and the threat of his friends getting caught in the crossfire pushes Touma almost over the DespairEventHorizon [[spoiler:resulting in him fully activating the Divider Zero, draining massive amounts of magic and life energy from everything around it, nearly scuttling the Huckbein airship, and causing emergency resuscitation for several of the people drained by Zero Effect his Divider created upon activation.]] Perhaps even more terrifying is Touma's lines just before this happens, showing just how far he's been pushed. [[spoiler:"Why is everyone doing such terrible things...to me and the things important to me? Everything that hurts. Everything that gets in the way. Fear, conflict, everything, and ''everyone''...should just '''''disappear'''''."]]
*** [[spoiler: And in the chapter after that, after getting loose, Touma contacts Fortis, the Huckebein's boss who managed to avoid the Eclipse Zero, and tells him in no uncertain terms that if he doesn't let his two friends go, he'll fire the same attack again, directly at the bridge.]]
** The original Reinforce comes across as pretty ExtremeDoormat most of the time, softspoken and obedient. The sound stages reveal that she is willing to let Hayate grope her breasts, and is willing to try to reach out and show kindness to Vita in spite of the latter's temper and angry rejections of her attempts. Reinforce very nearly destroyed the Earth because someone decided to greatly upset Hayate.
* ''Manga/MahouSenseiNegima'': Negi-sensei is a prime example. Normally the ten year-old teacher is kindly to the point of adorable, but in later chapters he has been a particularly ''awesome'' example of this trope. At one point, he finds that [[spoiler: three of his students have been enslaved, and one is being ''tortured by shock collars''. [[CrowningMomentOfAwesome Negi gives exactly one warning, and prepares to beat the guy to a pulp]] when he chooses not to listen.]] In addition, his acceptance of [[spoiler: the [[BlackMagic power of darkness]]]] makes him so fearsome that even his ''students'' are uneasy.
** There's also an incident where Satsuki freaks out a couple of guys who try to start a fight in her restaurant.
** Another incident where a group of girls are playing KeepAway with Negi's ring/secondary wand in the bath. One of them grabs it and dashes across the water (it's a ''big'' bath) on magic shoes, leaping high into the air to get away. Tall, quiet Akira, who was helping Negi look for it, ''catches'' her in midair, hurls her into the water, then does the same to everyone else who was teasing him.
** Chapter 265. [[http://mangafox.me/manga/mahou_sensei_negima/v29/c265/8.html HOLY SHIT]].
*** Chapter 292 squares [[HolyShitQuotient it]] with [[http://www.mangafox.com/manga/mahou_sensei_negima/v32/c292/19.html this]].
** Also, do ''not'' get Chisame pissed at you. [[spoiler: See that demon Negi in the link right above this? Rather than freaking out, she gets freaking angry at Negi for giving in to his dark side, while Nodoka and Kazumi struggle to keep him own she jumps in and ''[[GetAHoldOfYourselfMan slaps him]] [[http://www.mangafox.com/manga/mahou_sensei_negima/v29/c265/12.html upside the head]].'' Keep in mind that Demon!Negi was in an {{Unstoppable Rage}}/{{Roaring Rampage Of Revenge}}, tearing Kurt to pieces, and she stopped him ''dead'' in his tracks]].
** It has taken 280 chapters to get here, but we have finally found out what happens when you piss off [[ShrinkingViolet Nodoka Miyazaki]]. Nobody actually gets ''hurt'' in the process, but the {{Big Bad}}s' attack--until then verging on a CurbStompBattle--was stopped in its tracks, and is now presumably on its way to a complete reversal. [[AnyoneCanDie Good thing, too]].
** [[RobotGirl Chachamaru]] is a nice, soft spoken robo-maid, who has a crush on Negi. She can also [[spoiler: call down a massive blast of energy which can obliterate an extremely powerful summoned demon]] by using the power of...[[http://www.mangafox.com/manga/mahou_sensei_negima/v31/c281/15.html cats]].
*** Even if you can survive the KillSat, do not hurt her. [[TranquilFury Negi does]] [[http://www.mangafox.com/manga/mahou_sensei_negima/v35/c315/6.html not approve]].
* Joked around with in ''Manga/{{Mahoraba}}'' because it has two such characters. The first is Tamami who has her eyes closed and generally acts nefarious to the protagonist and to others. The second is the protagonist's teacher, Shirogane-sensei, who throws bad students into "[[SaunaOfDeath the Closet]]".
* ''Anime/MaiHiME'' positively ADORES this trope:
** [[TheOjou Polite and graceful]] [[SchoolgirlLesbians Schoolgirl Lesbian]] Shizuru Fujino had been nothing but kind and supportive to her best friend and object of her affections, Natsuki Kuga, for half of the show. Near the end, though, [[LoveMakesYouEvil that same love made her evil]], sending her on a rampage to eliminate anyone who came between her and Natsuki. Shizuru's fandom remained loyal, though irritated that the writers went a cliched route, and because it happened so close to the end of the series to have any real emotional impact. Consider for a moment that she [[DrivenToSuicide gets so depressed that she kills herself]] in the DatingSim based on the anime if the protagonist decides to wind up with Natsuki, and the previous event may not seem quite as ridiculous. Her [[EnsembleDarkhorse popularity]] possibly gives her ending a note of hope, though, as well as a more sympathetic role in ''Anime/MaiOtome''.
*** Killing '''herself''' over unrequited love doesn't necessarily serve as an indicator of willingness to ''kill other people'' over anything from actual threats to mere insults against Natsuki. Considering that Shizuru, in the dating sim, also [[spoiler:apparently killed Natsuki's mother]], the character may be different in that case, and there's more at play.
** Similarly, the normally [[{{Kawaiiko}} bubbly and cheerful]] Shiho Munakata lets her [[ClingyJealousGirl jealousy]] [[{{Yandere}} overcome her sanity]] after some pushes from [[spoiler: ManipulativeBastard Nagi]], eventually leading to a showdown with the female lead Mai [[spoiler: over a guy whom they ''both'' share as a [[LoveInterests Love Interest]]... leading to a no-win situation for poor Yuuichi. Who ends up pulling a HeroicSacrifice in the end to stop both Mai and Shiho from fighting.]].
** Oh, and Reito Kanzaki? Mai's ''other'' love interest? The soft-spoken guy who wears all black? [[spoiler:It turns out he's had the BigBad [[DemonicPossession living inside him for quite some time]].]] One PostEpisodeTrailer has Nagi [[LampshadeHanging lampshade this]] by saying something like "Come on...you mean to tell me he [[UnusuallyUninterestingSight didn't seem suspicious from the start]]?"
** Hell, ''[[TheHero Mai]] herself'' went into snap-out mode when she learned that [[spoiler:Mikoto's actions led to Takumi's death, although it later turned out that Shiho was responsible]]. When you see her biting her lip and drawing blood, you ''know'' you screwed up big time.
** Don't forget [[ManipulativeBastard Wataru]] [[ScaryShinyGlasses Ishigami]], [[NunsAreMikos Sister]] [[ArcherArchetype Yukariko]]'s controversial love interest. One of his earlier apparitions had him dorkily spinning around Mai's brother Takumi and begging him to be his model for his next painting... [[spoiler: And later he worms his way into Yukariko's heart, turns her against the other girls, harasses Yukino through text messages to break her and almost succeeds, etc.]]
** In the manga, Takumi, Mai's [[IllGirl sickly]] younger brother who's typically soft-spoken and considerate, [[spoiler:turns out to be the Obsidian Lord]].
* Haruka Minami from ''MinamiKe'' is actually the scariest character in the entire franchise... in addition to being a YamatoNadeshiko in development (and an OneeSama). She acts as a mother towards her two younger sisters. Remember how scared you got when you messed up & your mother lost her temper?
* ''Anime/MobileSuitGundamSEED'': Kira Yamato is generally a polite, soft-spoken person who cries easily, and as AllLovingHero, he's careful not to kill his enemies in combat, preferring to just disable their mobile suits, at least after he gets the [[MidSeasonUpgrade Freedom]]. However, when the BigBad [[ForTheEvulz needlessly]] [[StuffedIntoTheFridge kills]] his FallenPrincess ex-girlfriend Flay ''right in front of him'' (and right after they had just found each other, [[BreakTheHaughty after]] [[BreakTheCutie much misfortune]]), Kira chucks his [[ThouShaltNotKill "No Killing"]] rule out the window, resulting in a ''spectacular'' fight sequence that culminates with him ''ramming a beam saber through the villain's cockpit'' and leaving him in front of his KillSat as it fires.
** Another ''Gundam SEED'' example would be Miriallia Haw. As Gundam pilot Dearka Elsman finds out, Do Not make a snide remark to her when she's grieving and there is a sharp object nearby. You WILL regret it.
* ''Anime/MobileSuitGundamWing'': Quatre Raberba Winner is TheSmartGuy of the team, who is sweet, sensitive, and polite. But once he loses [[spoiler: his father and one of this sisters]] and the people in his colony turns against him, he builds a SuperPrototype HumongousMecha with two [[{{BFG}} Big Effing]] {{Wave Motion Gun}}s and goes into a TranquilFury, destroying an entire ''space colony''. [[spoiler: [[http://www.youtube.com/watch?v=dOaH0tsG3z0 Until he almost kills his best friend]]]].
** Building the Wing Zero was indeed the result of his going off the deep end and wanting to bring in an ultimate weapon to end the war. The resultant rampage (including the destruction of the colony), however, came about because he failed to realize why the design had been scrapped: the information overload of the cockpit caused a side effect of massive MindRape.
* Wolfgang Grimmer from ''{{Anime/Monster}}'' is possibly one of the nicest people you will ever meet... But do ''not'' upset him. [[StepfordSmiler Really]], [[UnstoppableRage don't]].
* ''Anime/MonsterRancher'': Golem is as gentle a giant as you could wish for and only really fights because he has no choice....but piss him off and it is [[spoiler: massacre time]].
** Genki might count too, it never really happened in-show, but we are talking about an innocent-looking eleven-year old who regularly kicks genetically engineered dinosaurs, {{Living Weapon}}s, and robotic stone dragons ''[[{{Badass}} in the face]]'' and will headbutt ''anything''. If he ever really lost it his general abilities, [[spoiler: coupled with the ending to series two]], suggest [[UnstoppableRage he would go absolutely]] [[SuperMode Super Saiyan]] on everyone and thing in his way.
* ''Manga/{{Narutaru}}'' loves this trope, but the best example by far would have to be the local LonelyRichKid, Hiroko "Hiro-chan" Kaizuka. She's a quiet {{Ojou}} in sixth grade who is mercilessly bullied at school over her excellent grades, while at home her parents berate her whenever she gets anything less than a perfect score on any test (even though she's pressured by the bullies to do badly lest they torture her more). She tries enduring this abuse as best she can while remaining unconfrontational, but when the bullies take their actions to ''monstrous'' degrees and her father tries cutting off her ties with her only friend... well, let's just say she puts her new [[{{Mon}} shadow dragon]] to ''very'' good use. The results are messy, to say the least.
* ''Manga/{{Naruto}}''. The title character, [[spoiler: who refused to give in to his emotions and extract vengeance upon the man who just [[MoralEventHorizon killed both of his teachers]] and [[AllYourBaseAreBelongToUs levelled his village with the ground]], in order to [[SlidingScaleOfIdealismVersusCynicism break the chain of hatred]]]] has [[SealedEvilInACan a malevolent, nine-tailed demon fox of immeasurable power sealed into himself]]--and this fox's power has a habit of seeping out of him whenever he loses his temper.
** Also, [[DarkMessiah Nagato]], [[spoiler: the man who levelled the title character's village to the ground,]] who was [[AllLovingHero unusually kind and sensible as a child]], but made a complete 180 after [[spoiler: he was given [[SadisticChoice the ultimatum]] of killing his best friend Yahiko or seeing his other best friend Konan get killed, and Yahiko forced his hand and made him take the former option, all this after Nagato had made it his purpose in life to [[LoveMakesYouEvil protect both of his friends, no matter what]]]].
** On the eve of the Uchiha Massacre, when those three Uchiha mooks confronted Itachi about Shisui's suspicious death and Itachi finally snapped, Itachi practically quoted this trope to them after he beat them all up in less than a second. Even afterward, [[ReverseMole Itachi]] still acted unfailingly polite in his screentime as an Akatsuki member. Though at this point most everyone already knew to beware him.
** [[TheBigGuy Chouji Akimichi]] and [[ShrinkingViolet Hinata Hyuuga]], two of the nicest characters besides the title one, also both quality for this trope. Hinata's timid, Chouji's placid, and both characters are extremely gentle and kind. However, harm the people they care about, whether by mocking and taunting them (Jirobo and Shikamaru, in Chouji's case) or [[spoiler: pinning them down and threatening to kill them (Naruto and Pein, in Hinata's case)]], and they will get angry. [[CrowningMomentOfAwesome Very angry.]]
*** The databook notes the stark change in Choji's personality by having two separate entries for him on the personality grid. Normal Choji is more toward the calmer and patient ends of the spectrum, whereas "Pissed" Choji is less so, and is one of the more passionate and less patient characters.
** Killer Bee is one of the nicest people in all of ''Naruto''. The idea of holding a grudge is completely alien to him. He also beat [[GodModeSue Sasuke]] to within an inch of his life after the later initiated an unprovoked attack on the former.
** Hell, Naruto's kinda full of these. Might Gai loves his students with a passion, always has an encouraging word and will believe in them no matter what. He'll also support them with every skill in his arsenal. Everything- including opening forbidden seals that tear his body apart even as he tears you limb from limb. Then there's the 3rd Hokage, who alternates between a listening ear, guiding council and all round badass who was the strongest ninja of his generation, and then, to a lesser extent, there's Kakashi. Calm, collected, slightly goofy and pretty much an all-round-nice-guy... until you do something to piss him off, and then he shows you exactly why he's the Copy Ninja whilst he's smearing your face in the dirt.
** A recent chapter has made, of all people, the God of Shinobi, Hashirama Senju, into this. His normal demeanor is, against all the legends and myths built up about him, very jovial, prone to outbursts of loud laughter, and not especially respected by even his younger brother. However, when the situation gets dire, his chakra aura becomes so powerful that just his glare starts destabilizing the foundation of a building, and everyone in a hostile environment is forced into a detente.
* When Nausicaa's father King Jhil dies in ''Manga/NausicaaOfTheValleyOfTheWind'', the kind-hearted princess becomes a murderous embodiment of berserker rage who appears to revel in slaughtering the enemy (one man in the manga, an entire squad in anime) until Yupa stops her. Afterwards, though, she is devastated by the thought that her heart could contain such rage.
** That's only in the movie. In the original manga, what sets her off is the Torumekians landing in the Valley without permission or quarantine (contaminating the Valley's crops and trees), having their knights attempt to pick a fight, defiling a grave Nausicaa dug, and [[ArsonMurderAndJaywalking bringing Worm-handlers into the Valley, whose slugs - attracted by the scent of the trinket Nausicaa is hiding - slither up her body]]. The result of her snapping is the same, though.
*** For the record, Jhil dies of natural causes almost halfway into the story, long after Nausicaa leaves the Valley; she doesn't even find out until near the end.
* At the start of ''Anime/NeonGenesisEvangelion'', Shinji Ikari is a loner and obviously has issues, but he's still generally quiet, kind and courteous. However, throughout the series, when the pressure on him proves to be too much, there's several occasions where he completely snaps and shows a violent, rage-filled side to his personality.
** Let's not forget that this manic rage is mirrored in his Eva's attitude, as Shinji goes insane with bloodlust, ''so does Unit 01'', [[spoiler:actually snapping off the limiters controlling it, after eating Zeruel]].
*** Well, [[spoiler: his mother's soul, a woman who is portrayed as [[YamatoNadeshiko nice, sweet, motherly and calm]] when we see her in the flesh, inhabits Unit 01 and is stated to be the reason behind the Eva's fits of insane and unstoppable rage, given that they always happens when [[MamaBear Shinji is in overwhelming danger]]]].
*** And then there's ''Anime/RebuildOfEvangelion''. Oh dear sweet hell, Shinji is an unstoppable force of nature who is so nice, even smiling despite his heartache. And then you threaten Asuka or Rei and he will redefine UnstoppableRage and RoaringRampageOfRevenge.
**** [[http://cjblackwing.files.wordpress.com/2010/06/eva-2-22-14207-shinji-spiral-power.jpg Holy Crap!]]
*** The dummy plugs are bloodthirsty berserkers, there's no doubt about that. However, they were based on [[TheStoic Rei]] and [[EnigmaticMinion Kaworu]]. Cue trope name.
* ''{{No6}}'': Sion. Just check out his reaction when Rikiga suggests Nezumi become a prostitute or when he [[spoiler: shoots a guy in Episode 10 for trying to kill Nezumi or in the novels when he nearly strangers a man for attempting to kill Nezumi]]. Nezumi even says Sion's not to be underestimated.
* ''Manga/OnePiece'': Monkey D. Luffy is generally a happy-go-lucky guy, and very cheerful... until you hurt his TrueCompanions, or his friends... or ''your'' TrueCompanions. Heaven help you if you do. It's about the only time that he ever takes off his NiceHat.
** Luffy's not the only Straw Hat that qualifies. Witness, Tony Tony Chopper the hyper-cute reindeer doctor, cute, innocent and cuddly one moment but make sure your will is updated before you decide to do something stupid like make him mad.
** This can qualify for all the Straw Hat Pirates, not just Luffy and Chopper; in spite of them being one of the most notorious crews in the world, they're all kindhearted and easy to get along with, albeit quirky, and they ''never'' throw the first punch. But provoking them too much is comparable to [[DigYourOwnGrave digging your own grave]]; each member of the crew could effortlessly and singlehandedly take out an army, and they would declare war on the entire world for the sake of just one of their friends. [[spoiler:And they did, and so far they've gotten away with it]].
** Special mention should go to Conis, a sweet girl from Skypeia who was introduced as a ProperLady-type character. After learning that her country's psychotic God-like ruler intended to destroy Sky Island and everyone on it and watching her father [[spoiler: seemingly]] get killed by said ruler, she ends up driving a ship into the Sky Guards, facing down an angry mob that refuse to believe her, threatening the Sky Guards with a bazooka, and publicly shouting heresy to convince them that their god has abandoned them.
** And, of course, we have Luffy's mentor, Red-Haired Shanks. Easily one of the most easygoing pirates in the world, he loves to party and is content to spend the whole day drinking away. He even shrugs off being physically abused, such as by having sake poured on his head. But like Luffy, he won't forgive anyone who hurts his friends. And he's ''not'' someone that you want to be a personal enemy of; he's one of the four strongest pirates in the world.
* Mitsukuni "Honey" Haninozuka from ''Manga/OuranHighSchoolHostClub'' is a short, blond cutie with a love of sweets and cute things, and is classified as the "[[{{Shotacon}} lolishota]] type" member of the club. [[OtakuSurrogate Renge]] cheerfully squeals about how he's so {{Moe}}. Harmless, right? [[KillerRabbit WRONG!]] Honey just happens to be [[CrouchingMoronHiddenBadass a black belt and heir to a family of VERY skilled martial artists]]. He's kicked the ass of grown soldiers twice his size, and strikes terror ''with a single look'' into the other hosts when they accidentally spill tea on his favorite stuffed rabbit.
** That's his dark side, Dark Honey.
*** For a good idea of his kickass-ness, he was asked by Japan's Secretary of Defense to not fight in public, for if other countries saw him, they might accuse Japan of housing a WMA (Weapon of Mass Destruction)...
** Don't forget Morinozuka "Mori" Takashi, Honey's cousin. He's usually very quiet, stoic, and passive... until he needs to kick ass. He's skilled in karate and judo, and is in fact a national champion at kendo. He and Honey make a formidable team.
* [[spoiler:[[ManipulativeBastard Jack Vessalius]]]] from ''Manga/PandoraHearts'' seems to be this way now in the latest chapters. It turns out that he [[spoiler:only pretended to be a nice, sweet man when in reality all he wanted was to cause the end of the world by bringing the world down for his posthumous love Lacie. All those things he said to [[TheHero Oz]], the [[DefrostingIceQueen Alice]] and everyone around him were nothing more than lies, if not half-truths.]]
** There's also Leo, who actually has a temper as bad as his master [[HairTriggerTemper Elliot]]. He just doesn't lose his temper as often since Elliot loses his own faster and that lets Leo regain his composure. Still doesn't mean that it's a good idea to try to piss him off, though. Also, it's generally a bad idea to try to cut his hair without his permission, which doesn't seem to ever be given, anyway.
*** [[spoiler:Then, there's the fact that he's the current Glen Baskerville.]]
**** Oz himself counts as well on numerous occasions. In Volume 2, when he's with the Intention and she mentions getting rid of Alice, he shoots her emotionlessly and smiles. In Volume 3, he throws a huge fit at William West, who is killed by Vincent anyway. [[spoiler: In Volume Five when he witnesses Alice's death, he goes absolutely INSANE and decides to destroy everything that makes Alice sad. He then goes on to say he'll destroy Alice, too. *In Volume 13 is probably where we see the normal, happy-go-lucky, carefree Oz at his scariest. Basically, the villain has hauled off his best friends to be murdered and intends to kill all the innocent people at a party and lied to his followers and believes religion is "just a way to brainwash" and decides to throw people down into the same hell he escaped from. Elliot (who is notable for having a [[ tendency to flip out over the littlest of things HairTriggerTemper)points out that he thought Oz sounded off even though he said he was okay. Oz says he'll never forgive Yura or his dumb rituals....he'll lay waste to it all himself. The background shows Oz, though tranquil, as incredibly angry, and Elliot is scared. Let me repeat:usually, Elliot is scaring the crap out of meek, mild-mannered Oz by yelling at him, but if suddenly he's scared, beware.]]
* From ''{{Anime/Pokemon}}'': Ash's Pikachu. [[http://i256.photobucket.com/albums/hh167/irothtin/vlcsnap-9229146.png No, really]].
** Pikachu's power level tends to fluctuate depending on the episode. Most of the time it's a PintSizedPowerhouse, but there have been a few [[AssPull Ass Pulls]] like the time it lost to a ''[[ComMons Snivy.]]''
** There's also a Dragonite in one of the later Johto episodes that goes BATSH*T CRAZY after the Team Rocket trio grabs the IdiotBall ''again'' and decides to steal a relic that it was guarding, resulting in the Dragonite destroying a significant portion of the garden it lived in while in an UnstoppableRage. This turns into a TearJerker in the end, as after Dragonite snaps out of it and realizes what it's done, it breaks down crying. The worst part? Dragonite are normally '''FRIENDLY'''.
** As of ''Best Wishes'', Cilan. When he gets genuinely angry, '''he really gets angry.''' [[spoiler: Though his flip-outs have been mostly played for laughs]].
** It's not limited to heroes: James of the Team Rocket trio has typically been characterized as more pleasant and cheerful than his teammates, and a borderline ExtremeDoormat to boot. He's only had ''two'' real flip-outs...one of which involved him trying to '''steal a skyscraper''' [[DisproportionateRetribution because his bottle cap collection had been stolen]]. The other had him ''attack'' Jessie and Meowth when they refused to team up with Ash, even though [[PapaWolf there were baby Pokemon--including James' Mime Jr.--in danger.]] Both of these happened ''before'' Team Rocket TookALevelInBadass.
* In ''Manga/PokemonSpecial'', Yellow is everyone's friend. But if you threaten her forest in ''any way'', you will be thoroughly stomped on by her usually-normal Pokémon roster... boosted to the mid level-80's on good old Viridian ragepower. Good luck, you'll need it!
* Sasame from ''{{Pretear}}'' is one of the kindest members of the Leafe Knights. He's always supportive towards [[MagicalGirl Himeno]], tries to be the voice of reason among the older knights and resolves fights...[[spoiler:And he's secretly in love with the DarkMagicalGirl. When he realizes that she can't turn from the dark side, he snaps, performs a FaceHeelTurn, and then tries to kill the other knights under her orders.]]
* Gentle, selfless, fatherly [[NonActionGuy Shuuichirou Oishi]] from the ''Manga/PrinceOfTennis'' is pretty much the TeamMom of the Seigaku team. But press the ''very'' few buttons he has? Let's just say that pretty much ''[[UnstoppableRage no one]]'' [[UnstoppableRage can stop him]] in the two or three times he loses his patience on you. Well-shown when his beloved partner Eiji says something insensitive about him in public ''and Oishi screams and tosses Eiji to the ground.''
** And it's not only Oishi, either! [[EyesAlwaysShut Shuusuke Fuji]] also looks and acts cheerful, pleasant and polite, but if you do anything to piss him off (especially if you hurt/threaten his friends [[BigBrotherInstinct or his little brother Yuuta]]), you should ''pray'' he's not your next tennis opponent or isn't near to you for quite a while.
** Outside of Seigaku, there's little Data Player Taichi Dan from Yamabuki. Sweet, feminine-looking, naïve, etc - and is capable of yelling at [[{{Jerkass}} Jin Akutsu]], one of the most violent players in the whole circuit. Dan can be said to be Akutsu's KidWithTheLeash, in a sense.
** Not to mention Seiichi Yukimura of Rikkaidai. He looks feminine and kind, is very polite and soft-spoken, and strongly reminds you of [[YamatoNadeshiko the perfect Japanese woman]]... but he turns into a [[spoiler: {{Knight Templar}} once he's on the court, by making his opponents lose their hope of winning]]. Need I say more?
** Saki, one of Kozue's alternate personalities, could arguably apply, though she wouldn't necessarily become a threat to health and sanity. Her BreakTheCutie threshold is insanely low.
* Explicitly parodied in ''Manga/RanmaOneHalf'': when the family is convinced the normally serene and placid Kasumi has finally snapped after they thoughtlessly go out to dinner without her and return to find evidence of a major psychotic tantrum. They're on the verge of "sacrificing" Ranma to appease her anger when it turns out the damage was all from Kasumi's attempts to capture a cat that had gotten into the house.
** Used straight in the "Evil Ogre" {{manga}} arc and "Faster, Kasumi! Kill, kill!" {{OAV}}: When Kasumi is possessed by a vengeful ogre that makes its host act on their "most evil desires" everyone is terrified by the possibilities as she sweetly goes about adding little evil twists to her normal daily routines. Fortunately Kasumi's most evil desires don't extend much beyond spreading tacks in her father's bedding, embroidering "Okama" ("queer") on the back of Ranma's shirt, ordering tons of expensive takeout food inappropriately early in the morning and cutting cloth dolls out of the sheets.
** FanFic writers seem to like this trope in regards to Kasumi.
** Ranma's mother Nodoka Saotome is a rather nasty swing on this trope. She's a kindly, sweet woman whom both Ranma and Akane look up to, with the latter being implied to consider her almost a substitute mother... however, she is even more prone to put HonourBeforeReason than any of the other cast members. Even though the {{Seppuku}} pledge her husband made is so vague that nobody else would even consider it to be worth the paper it was scrawled on, she's so devoted to it that she carries a sword everywhere she goes, just in case she meets Ranma and she decides he's unmanly. And that means ''everywhere''- she's even shown sleeping and bathing with it. And it doesn't exactly take much for her to start pulling it out, either.
** Ranma himself, despite being a [[JerkWithAHeartOfGold jerk]] can fall into this category. Under normal circumstances, Ranma is a rather cynical, reserved un-socialized jerk, but despite his tendency to insult people, usually by accident and being [[NoSocialSkills unaware of normal social mores]], will go out of his way to even help people that have in the past tried to kill, humiliate and/or rape him/her. If you want to know the result of getting Ranma actually angry, all you have to do is ask Saffron what made him re-incarnate most recently.
*** Heck, his opening move in that fight was to slice off Saffron's arm, whereas up to this point he was one of the few characters tended to go out of their way not to use maiming or lethal force. Do NOT endanger Akane.
* In ''RODTheTV'' it is eventually revealed that this happened with Yomiko and the Library. Joker kept pushing her and, when he finally revealed what he'd done to her lover... let's just say there's a reason you don't antagonist a Papermaster inside a ''library'', especially [=THE=] Library.
** Sena is generally a NiceGuy with being a bit of a coward. But insulting his teammates is one way to [[BerserkButton tick him off]] and you'll pay a heavy price.
* ''Manga/RosarioToVampire''
** San Otonashi, a sweet, little girl (okay, [[OlderThanTheyLook not really that little]]) who [[CuteMute doesn't speak]] and hates confrontations. [[spoiler:She's not ''incapable'' of speech; her muteness is a conscious decision. Her monster identity is a [[GreekMythology siren]], so her voice ''[[MakeMeWannaShout kills people]]''. A villainous siren learned this hard way, as she gave off the impression of only singing a defensive song to protect her friends, when in fact she'd been singing another song ''at a pitch too high to be heard'' that was tearing him apart from within.]] Later, in the final arc of the series [[spoiler:she is fighting on par with two of the Dark Lords, the strongest monsters who once defeated the BigBad and sealed him years before]].
** On the same note, after Tsukune gets his '[[SuperpoweredEvilSide upgrades]]', it's generally not a good idea to bait him by [[TooStupidToLive attacking]] his friends. And now he got those 'upgrades' under ''complete control'', [[TranquilFury hoooo boy]]....
** Outer Moka is herself no slouch; in the second chapter of the series, she ''defenestrates Kurumu'' upon learning from her other self how much of a bad idea leaving Tsukune alone with a succubus really is.
* ''Manga/RurouniKenshin'' has Kenshin Himura. The guy is a soft-spoken MartialPacifist whom his girlfriend occasionally hits, and always tries to talk first and only attack later. But do ''not'' piss him off enough to have the Battousai, his SuperpoweredEvilSide of sorts, come out. We warned you.
* ''Franchise/SailorMoon'':
** Hotaru Tomoe fis a nice, peaceful girl... who can beat the demons just by looking funny at them.
** Ami Mizuno/Sailor Mercury might be a shy little CuteBookworm, but on two separate occasions, one being an incident where the monsters attacked a daycare, and the other where a monster who Ami thought was a rival in academics, she managed to unleash hell on either enemy.
** Despite her being a HugeSchoolGirl, Makoto Kino/Sailor Jupiter is a NiceGirl who cares immensely about her friends, even going as far as to donate blood to an injured old friend. Do NOT attack Usagi, lest you be on the wrong end of a CurbStompBattle, even with her being anemic from the blood loss.
* Andromeda Shun of ''Manga/SaintSeiya'' is a TechnicalPacifist and is, on more than on occasion, called the kindest and gentlest of the five main Saints. He's the kind of guy who begs his enemies not to fight and lets them beat him within an inch of his life rather than fight a battle he doesn't believe in. That is, until you try to kill one of his friends. And lord help you if you're the bastard who [[Main/YouKilledMyFather murdered his teacher...]]
** This trope is also the hallmark of the various incarnations of Hades, God of Death, mortal rival to Athena, and the instigator of the various Holy Wars throughout history. [[spoiler: Andromeda Shun is the newest incarnation of Hades in Saint Seiya]]. Meanwhile, in the prequel series Saint Seiya: The Lost Canvas, [[spoiler: a meek to a fault young boy named Alone is Hades' next vessel]]. [[spoiler: He is the best friend of the current Pegasus Saint, Tenma, as well as the current incarnation of Athena, Sasha]]. His first act upon his transformation to Hades is to burn down their home town and massacre everyone in it.
* Cho Hakkai in ''Manga/{{Saiyuki}}'' is polite and quiet-spoken and generally the nicest of the protagonists... unless he's pushed too far. When he really lets loose, he terrifies even makes-the-gods-nervous Goku. Sanzo has no qualms about taking on Goku or Gojyo in a tournament side chapter, but is nervous at the idea of facing Hakkai without his sutra.
* StepfordSmiler Kafuka Fuura from ''Manga/SayonaraZetsuboSensei'' hides a bloodlust that makes those who are acutely aware of her cheerful facade mortally terrified of her. Her classmate Meru takes one look in Kafuka's eyes and is confident that one day, she will [[KillEmAll kill them all.]]
* ''VisualNovel/SchoolDays'': Makoto Itou [[KarmicDeath really]] [[OffWithHisHead had it coming]].
* ''Manga/SetoNoHanayome'' inverts this with Maki, who's introduced as a sweet, incredibly {{Moe}} character. Then as soon as she's alone with Nagasumi, she reveals herself to be a battle-hardened (and [[{{Yandere}} psychotic]]) assassin on a mission to kill Nagasumi.
** Played straight with San, who's usually a YamatoNadeshiko, but ''will'' screw you up with her "Voice Shockwave" ability. She's also a proficient swordsman.
* In a flashback, we see [[{{Yandere}} Kaede Fuyou]] from ''VisualNovel/{{Shuffle}}'' go off the deep end on the male lead after her mother's death (''Boxcutter Kaede''), an effect that is repeated near the end of the series when the lead starts seriously going out with another girl. Kaede and the lead, Rin, have effectively been living as husband and wife for close to ten years, which can be seen as Kaede [[TheAtoner trying to repair the damage her other self caused to Rin]].
* Nadeshiko Fujisaki of ''ShugoChara'' sweet, calm, polite, and all around pleasant...that is, unless, [[BerserkButton you happen to spark her character change]]. Note: [[spoiler: I know Nadeshiko is actually a boy but I don't want to spoil people who don't know this yet]]
* In ''Anime/SoRaNoWoTo'', Filicia is the [[Creator/AyaEndo soft-spoken]], [[{{Meganekko}} glasses-wearing]] TeamMom. Well, as long as you don't threaten or abuse any of her squad members, [[MamaBear which'll make her remind you that she is after all a Lieutenant of the Helvetian Army]] and [[ShellShockedVeteran a survivor of the battle of]] [[InferredHolocaust Binnenland]].
* Tsubaki from ''Manga/SoulEater'' is usually [[HumbleHero shy and humble]]. Thus, when she finally and truly stands up for herself in the fight against [[spoiler: her brother]], [[ActionGirl the result]] was pure [[CrowningMomentOfAwesome awesome]].
** Similarly, this series' personification of Death is not only a good guy, he's funny-looking and goofy -- [[spoiler:but that's just a form he uses to avoid scaring his students. ''Pity'' the villain who's dangerous enough to make Shinigami-sama go old-school.]] The last guy who did that [[spoiler:had his skin ripped off in one pull and then he was forcibly cocooned inside it.]] *shudder*
** Same goes for Demon Hammer Marie Mjolnir, [[SilkHidingSteel a lovely, sweet lady who is also known as the 'Crushing Weapon']] for a reason. When confronting the murderer of BJ, [[spoiler: Justin Law, she reacts to the possibility of him harming her students by landing a punch on his chest so hard he's thrown into the air. This comes after Justin, having clearly forgotten what series he's in, points out that though he and Marie are both Death Scythes, she has only a "woman's power".]].
** Spirit shows hints of this when he loses his temper with Medusa.
** Patty's TheDitz, but she's a better fighter than she looks. She grew up on the streets, surviving by helping her older sister Liz mug random people. [[LetsGetDangerous When she gets serious]], she is ''much'' more horrifying than her DeadpanSnarker sister.
* Wako Agemaki of ''Anime/StarDriver'', the ever peppy south maiden, had never had a ''true'' moment of rage during the show. Then came Episode 19. When Glittering Crux member Kou takes over Takuto's body, and tries kissing her. Something Takuto would never do. Did we mention it was her birthday? She puts Sugata's knife to her throat, complete with DeathGlare, and drawing a little blood, and tells her, in no uncertain terms, it doesn't matter if she's controlling his body. She ''will'' cut her.
* ''Manga/SteppingOnRoses'' has several characters that start out as kind and caring, but through the series' events become deceitful, manipulative, or even all-out crazy... The most notable example of the latter is [[spoiler:Nozomu]]. On the other hand, [[spoiler: Nozomu's arranged fiancée Miu]] turns out to be ''very'' scary after being subjected to some dashes of the BreakTheCutie...
* Eto Kai from ''Manga/{{Switch}}'' is typically [[TechnicalPacifist very gentle and kind]], however, if you even think about [[BerserkButton harming Hal]], you'll find him significantly less agreeable.
* A recurring theme in the ''Anime/TenchiMuyo'' universe. The main characters of the series set in this verse are all unassuming {{Nice Guy}}s. In the main continuity, their household is explicitly stated to be the single greatest concentration of Power in the entire ''universe''. Make them angry and they will ''end you''.
* Don't mess with [[Anime/TengenToppaGurrenLagann Simon the Digger]]. Seriously, don't.
** Don't forget Nia! For the bulk of the series, she's just about the nicest, politest, most innocent character in the entire show. Until you find out she's actually [[spoiler:an Emissary of the Anti-Spirals, in charge of the extermination of Mankind.]]
* Mikael from ''TenshiNiNarumon'' is usually an epitome of calmness, kindness and politness when dealing with strangers and people he's not close to, unless he's with Raphael--[[spoiler: then he's just a very stubborn, irritable and insecure boy. But when the stress proves to be too much for him and things are not going the way he wants them it tends to NOT end up very well]].
** Mama is usually a kind and carefree house lady [[spoiler: that is until the stress of housework starts to wear her off and she decides she wants to chill herself out with some broom-flying. Or when she comes across something round - just RUN!]]
*** Miruru looks like a cute, harmless cat-girl and acts like a total ditz most of the time [[spoiler: but at least in the first season she was one of bad guys' henchmen and did some pretty nasty things. She GOT Better but her selfish attitude didn't really changed]]
**** Muse is totally moe and looks like she's always on the verge of crying, [[spoiler: but being one of Silky's henchmen means she's also actively plotting how to prevent Noelle from becoming an angel - although it's true that she did most of it for Eros]]
***** Sara [[spoiler: when dieting like crazy]].
****** And also Ruka [[spoiler: beating poor Eros to death in Episode 19]]
* Keima's mother Mari, from ''Manga/TheWorldGodOnlyKnows'', is a nice, simple Japanese housewife. Then [[PrettyFreeloader Elsee]] pretends to be her husband's illegitimate daughter, and we find out she used to run with biker gangs...
* ''Manga/TowardTheTerra'' has the Mu. They are a peaceful race of humans with [[PsychicPowers psychic powers]], who are hunted down like animals and chased across the galaxy due to FantasticRacism and DeusEstMachina. Seeing [[spoiler: their new home [[EarthShatteringKaboom destroyed]] along with their fellow Mu, whose [[{{Synchronization}} telepathic scream they can hear]]]], makes the survivors declare war on humankind and turns their leader into TheUnfettered. They successfully conquer one world after another, leaving planetary defenses completely shattered, until humans finally mobilize all military forces and invent anti-Mu weaponry.
* ''Manga/{{Trigun}}'''s Vash the Stampede is the sweetest, most gentle, peace-loving guy you could ever wish to meet, and manages to stay so despite all the horrible things that keep happening to him, and acts like a complete goofball most of the time when he's not angsting. He [[BadAss regularly manages to defuse dangerous situations and deal with opponents with minimal force, and sometimes without even having to fire his gun]], despite the fact that if he really felt like it, he could easily unleash holy hell on everyone around him and pretty much nothing would be able to stop him. But if you do what Monev the Gale did, like blow up an entire city block and kill dozens of people in an attempt to kill him... well, the good news is, [[TechnicalPacifist he won't kill you,]] but the bad news is, [[UnstoppableRage you're still utterly screwed.]] The scene when he looms up out of the darkness with an expression of pure rage on his face and [[GlowingEyesOfDoom his eyes glowing solid blue]] is chilling. He then goes on to completely thrash Monev [[CrowningMomentOfAwesome using a vault door, the last three bullets in his revolver, a shot from the literal]] [[HandCannon Hand Cannon]] [[CrowningMomentofAwesome in his cybernetic left arm, and a solid boot to the face]], and reduce the huge, previously unstoppable assassin to a blubbering mess on the ground, begging for his life (and Vash was damn well considering putting a bullet between his eyes too).
** Notably, Vash ''did'' shoot to kill after Monev blew up the block. Viewers here a single gunshot and suddenly there's ''three'' bullets in Monev's helmet. The only reason he lived was that apparently his visor was bulletproof.
* [[WinterRoyalLady Ooyuki]] from ''Manga/UruseiYatsura'' is [[YamatoNadeshiko kind and gentle]] in the extreme, if rather stingy. Once, Ran thought she had pissed Ooyuki off and was so scared she ran, throwing live bombs and grenades after Ooyuki just to buy time to escape. Ooyuki seemed completely unbothered and the friends made up... ''however,'' Ooyuki did give a stern (but softly spoken) lecture to the king lemming who had trashed Ran's place in the meantime, and the lemming ran off. [[GlowingEyesOfDoom Ooyuki said]], "Oh? Do you think you can run away?" The [[AnIcePerson resulting punishment]] and ''collateral damage thereof'' caused no small amount of mental trauma to the lemming and any witnesses.
* ''Manga/YakitateJapan'': Kirisaki Yuichi. Only in episode 1 though. The rest, he acts as Pantasia's Main Branch antagonist and wishes to crush the "cockroaches" (that is Azuma's gang of the southern branch).
* Komachi in ''Anime/YesPrettyCure5'' is easily the most passive member of the cast, [[BarrierWarrior and her power is just a shield.]] Near the end of the series, someone manages to ''really'' piss her off. Turns out that shield can be used as an offensive weapon after all--and she carves out an interesting new feature in the landscape.
** In general, ''Anime/PrettyCure'' does it with just about every one of its [[LoadsAndLoadsOfCharacters many]] [[MagicalGirlWarrior Magical Girl Warriors]]. Several of the franchise's villains have even been ''KilledOffForReal'', and many SugarWiki/AwesomeMoments were had because of this. When you hear "ThisIsUnforgivable", expect this trope to come ''very soon''.
*** This was ''supposed'' to be Alice's schtick in ''Anime/DokiDokiPrettyCure'' in that she's a very nice person with a ''very'' short temper, however due to certain tropes coming into play, what could have been BullyingTheDragon turns into PokeThePoodle.
* Misa Anehara from ''YokuWakaruGendaiMahou'' is usually laid back and playful but is actually one of the most powerful modern-day magicians and deadly when serious.
* [[Anime/YuGiOh Yami Yugi]] was never that patient with his opponents, but at least he tried to take a kinder route to defeating them, even if they threatened his friends. However, when he lost the soul of his partner, and local JerkAss Insector Haga tricked him into believing he had torn up the card that held it during their duel on a train during the DOMA arc...well, let's just say that it's a good thing that duels are ''supposed'' to end when a player's life points hit 0.
** The episode after that one when Yami Yugi "meets" Yugi's lost soul in a kind of cursed land--and Yugi forces him into a duel, all the while snapping accusations at the pharaoh, and throwing Yami's earlier, cruel tactics right back at him. It was a being cruel to be kind-type situation, but the fact that Yugi could be that harsh ''at all'' was a shock to many fans.
** Let's not forget the original Season Zero either, where Yami Yugi, in the first five episodes, sends all the bullies insane/in the Shadow Realm/dead/blown up(ok, ''that'' one was in a separate episode, but still...)
* Yuki Judai from ''Anime/YuGiOhGX''. Completely lovable guy who gets along with everyone, including people who have tried to kill him: right up until five of his best friends end up dead (or so he thought at the time). Cue UnstoppableRage on Brron and the advent of Judai's "if I have to be evil to stop evil, then I will be" philosophy.
** And then he proceeds to conquer most of Dark World and suck up living souls to fuel Super Fusion with a loyal army of monsters at his beck and call. Brr.
* In ''Anime/YuGiOh5Ds'', Carly Nagisa is a sweet, eccentric girl whose love of TheLancer Jack Atlas is incredibly cute. However, [[spoiler: when she gets tortured and then killed in a Psychic Duel trying to get information about the Arcadia Movement to help him, she turns into a Dark Signer]] and unleashes a certified, factory-sealed can of whoop-ass on [[spoiler: her murderer, Divine, for robbing her of a chance to be happy with Jack.]] This is done in a fashion that would be horrific if the bastard didn't completely deserve it.
** Somehow, [[spoiler: Divine survives the whole thing,]] but still. ''Dang.''
* Kurama of ''Manga/YuYuHakusho'' is generally polite to everybody else and arguably the nicest member of the cast... unless you piss him off [[EvenBadMenLoveTheirMamas (threatening his mother is a good way to do that)]]. Then he will kill your ass in very brutal and bloody way that involves [[GreenThumb lots of pretty flowers.]] [[LotusEaterMachine Or]] [[FateWorseThanDeath worse.]]
** Hiei noted this in an early arc, saying that Kurama's [[TranquilFury calm mind allows his be as calculating and brutal as he wants]] without being distracted. He even says that, back when he was a PsychoForHire BigBad, he brought Kurama along as a partner to avoid gaining his ire in the future.
** [[spoiler:And in the Dark Tournament someone plays on his sympathy for an early lead and regresses his age back from his normal form all the way back to infancy and ''then'' to Yoko Kurama. Bad move there, buddy]].
** And this is reinforced in the Chapter Black arc, where [[spoiler: his opponent was a CreepyChild, and they were in a DeadlyGame. He was forced to ShootTheDog and was most upset about not being able to avoid killing the kid. Then he found out that his next rival was NOT who he seemed... It's a FateWorseThanDeath for you]].
** Yukina is the one confirmed genocidal character in the show; she blames the other ice maidens for her mother's death, and wishes her brother would kill them all.
* Shiho from ''ZettaiKarenChildren'' gets more and more aggressive tendencies as the series progresses--sometimes to sadistic levels. You ''really'' don't want her to use her telepathic abilities on you when she is in one of those moods.
** Episode 40 confirms that this applies to Minamoto as well. Piss him off and you risk ''[[spoiler: getting a bottle smashed against your skull]]'' or having him ''[[spoiler: remotely operate a giant drill vehicle and demolish the premises]]''.
* Hatou from ''Manga/MurasakiiroNoQualia'' is a very laidback character. That is, until [[spoiler:[[KillTheCutie Yukari dies]]]].
* Nagisa Shiota from ''Manga/AnsatsuKyoushitsu'' is a nice guy but he is also the most dangerous student in Class-E due to his stealth and bloodlust. He's not violent or anything, he just has no compunction against killing people.
* Gabu from ''Literature/ArashiNoYoruNi''. [[NobleWolf He may be a sweet, kind, and caring wolf]], but keep in mind that he is a ''wolf''. When pushed past the breaking point, he will take an entire pack down.
* Jeanne, leader of the X-Laws in ''Manga/ShamanKing'', is a small 11 year-old girl gifted with IncorruptiblePurePureness and huge amounts of charisma, who manages to win over almost everyone who meets her (at least initially) with her selflessness and grandiose speeches about justice and peace, and she's also on a mission to kill BigBad Hao Asakura. She's also a KnightTemplar supreme (in charge of an entire organization of {{Knight Templar}}s)) who messily executes her opponents with giant torture devices (and even spends most of her time locked in an iron maiden, and her Over Soul has her attached to various torture devices as well.) There are no EnemyMine agreements to be had with her, either. Either you're an X-Law, or you're the enemy, and will probably meet the same bloody fate as Hao's forces if you have to go up against her.
* Yuuri Shibuya from "LightNovel/KyoKaraMaoh" is a 15 year old high school student who is dragged into an alternate fantasy world and made the king of demons. He is fairly average, kind, considerate, even tempered, and doesn't really stand firm. However, he has the ability to use extremely powerful magic that is activated when he becomes extremely emotional. When he does reach this point hes suddenly an extremely stern and violent alternate ego that can control water and other materials to his bidding.
* [[TheHero Tsukihiko Fujiki]] from ''Yuusen Shoujo - Plug In Girl'' is basically what happened if [[BewareTheNiceOnes/VisualNovels Shirou]] [[VisualNovel/FateStayNight Emiya]] is learning [[{{Cyborg}} cyborg science]] instead of sword magic and [[{{Keet}} a lot more cheerful]]. He's [[AllLovingHero kind, considerate,]] all around NiceGuy. However, [[ChronicHeroSyndrome if he sees anyone in danger,]] [[DeclarationOfProtection he'll protect them.]] Considering most of his upper body is made of [[MinovskyParticle psycho]][[GreenLanternRing material]], [[PhotographicMemory he can copying any weapon he understands]] and [[BadassBookworm he can be...]] ''[[CrazyEnoughToWork creative]]'' [[TheEngineer when utilizes it]], all his fight tended to end in his favor. [[HourOfPower As long as he has enough stamina]].
** The first guy who defeat Tsukihiko, Yuuto Ryuuzouji, also the prime example of this. A small, unasuming boy with [[NiceGuy kind personality]], [[TechnicalPacifist hates confrontation]], and [[NeverHurtAnInnocent don't like hurting innocents]]. [[spoiler:Then it's [[{{Subversion}} Subverted]] with his SuperpoweredEvilSide, who is [[{{Jerkass}} caustic]], [[CombatPragmatist brutal]], [[PsychoForHire likes violence,]] basically everything his other personality isn't. Then ''DoubleSubverted'' with the "nice" Yuuto, who actually is personality created for front for social situations. [[DisabilitySuperpower Because of his status as created personality,]] [[BiggerStick he can have his body stuffed with psychomaterial up to 85%.]] And ''exactly'' because his niceness, [[IDidWhatIHadToDo he didn't hesitate to brutalize enemies so thoroughly if said enemies happened to stand in the way of his objective, so that the fight can over quickly.]]]]
* Spike from ''Anime/CowboyBebop'' is apparently just a lanky carefree dude with a very zen attitude to life, fairly friendly and good-hearted. What he isn't telling you is that he's a master martial artist and gunslinger supreme, and the reason he's so zen is because [[spoiler:he considers himself already dead, so he ''never'' holds back]]. Annoy him enough and he'll beat you senseless without breaking a sweat. Harm someone he loves and he'll return the favour tenfold. ''Kill'' someone he loves and [[spoiler:he'll annihilate an entire army to get to you and then kill you, even if it costs him his life]].
* Weed of ''Anime/GingaDensetsuWeed'' is a very pure, sweet and small adolescent Akita/Kishu mix, but he proves to be one of the [[PintSizedPowerhouse best fighters]] in the series. When a packmate defies his orders and kills two of his enemies against his wishes, he bites the dog, who is a powerful [[spoiler:Germain shepherd]] by the way, on the neck and tosses him away. He also holds his own against a [[spoiler:Great Dane]] that dwarfs him, talking advantage of his speed and his ability to perform the Battōga, a attack that came from wolves. Being the [[InTheBlood grandson of Japan's greatest bearhound]] pays off.

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