Dragon Ball Z: Gohan. Though suffice to say, nearly every Saiyan character qualifies at one point or another. But Gohan is the outlier, because his potential since the beginning was defined as Unstoppable Rage.
Goku's first Super Saiyan transformation also qualifies. He's out of power, then has to watch Piccolo, his rival and valuable ally at the time, and his best friend, Krillin, both get attacked by Freeza, with Krillin murdered outright — and then, just to be even more of a monster than he already is, Freeza just has to threaten little Gohan as well. This pushes Goku over the edge.
Broly, the Legendary Super Saiyan, with a legendary hatred of Goku to match. If you so much as look like Goku and you're in Broly's vicinity, run. He'll kill you regardless of who you are, but if you're Goku, he'll make you suffer first.
In Dragon Ball Z: Battle of Gods, when Vegeta sees Beerus slap his wife Bulma, he goes absolutely ballistic: not only does he give Beerus a run for his money for the first time since his coming to Earth, but his power level actually exceeds Goku's for a moment!
In Resurrection F, this trope sums up Frieza's whole mindset. His final Villainous Breakdown really sells it. Although it at first manifested as Tranquil Fury, his hatred of Goku and (even more thanks to Hell) his Ax-Crazy nature quickly pushes him past all restraint and goes all out.
Sonic X in its third season had the eponymous character Sonic at one point absorb negative energies from fake Chaos Emeralds which unleashed when he became angry upon seeing his friends badly beaten and at risk of execution. The resultant fight involved him beating the everloving crap out of two robots specifically designed to be difficult to defeat. His long-time nemesis, Dr. Robotnik/Eggman, convinces him to stop his rage.
Starscream in the Unicron Trilogy gets a couple of these. The first time occurred in Transformers Armada after learning that Megatron was plotting to terminate him and replace him with Thrust as the deception's second in command. He got pissed off, powered up, and defeated most of the other Decepticons and defect to the Autobots (for a while). 20 years later in Transformers Cybertron, he does it again, this time, to the Autobots. He had just betrayed Megatron (again) and has finally obtained an army of his own. What does he do when the Autobots came for the Cyber Planet Keys and the Omega Lock? He goes on a foe-charging attack and defeated and/or almost killed several Autobots. Damn...
Naruto has the Nine-Tailed Fox form that Naruto engages during instances of extreme emotional disturbance. The first time is when Sasuke defends him from Haku's lethal technique, followed by several later instances when Naruto is angered, and culminating in the near-complete release of the Fox after Hinata's apparent death. The Rage will inevitably cause Naruto's lifespan to be shortened, due to his constantly dying/regenerating cells while the form is active. Also, if Naruto completely loses it, the Fox will take possession of his body. No longer need to worry about it since he has full control over Kurama.
Before Rin's death, Obito is a fairly average ninja who's missing a right arm and a left eye. After he watches her die, he gains Mangekyou Sharingan and uses it to absolutely slaughter Rin's killers, in what can only be described as one of the series' most brutal fights. He leaves a literal lake of blood in his wake.
Orochimaru invokes this trope. And boy does he not learn his lesson.
Subverted in Okami-San: when Ryoshi first fights Shirou, his attempts to attack are easily thwarted; later, while training, he learns that if he gives in to the anger he becomes predictable, blind to his opponent's movements, and generally far easier to beat.
For Code Geass, with all a lot of characters being over-protective of another, this happens a number of times. Suzaku stands out particularly, despite being two-thirds pacifist and displaying warrior-like grace, the moment when he witnesses Euphy being shot causes him to go berserk, charging through the battlefield and through two mechas that posed a serious threat to him in order to rescue Princess Euphemia following which he abandons the battle entirely. This later seemingly pushes him past his Despair Event Horizon.
Ranma ˝: gohA more comedic use of the trope, if Ranma's fear of cats reaches a critical point (especially when surrounded by them and unable to get away), his mental state becomes like that of a cat. He can only use the Neko-ken (cat fist) when in this state, which manifests as an increase in speed and agility, and the ability to attack enemies (or anything else that annoys him) with invisible claws sharp enough to slice through seemingly anything. But with his mind and personality those of a common cat, this also becomes an example of Sanity Has Advantages: Ranma is distractable, unfocused and generally stupid in this mode, meaning that he can be outthought fairly easily. In this state, Akane finds herself the Kid with the Leash, as Ranma will joyfully savage his/her own Jerk Ass father without a second thought, but he curls up with her like a happy kitten, even though he is insistent that She Is Not My Girlfriend.
Ryoga also qualifies during the "Shi Shi Hokodan" story arc, where he learns a Kamehame Hadoken attack powered by negative emotion like depression and anger. He finally perfects the attack by reaching his lowest emotional point, Akane saying she hates him, in which it becomes a Sphere of Destruction.
In Princess Mononoke, this happens to Nago and almost to Okkoto, who are rhinoceros-sized wild boars to begin with. Their rage comes from their whole tribes being slaughtered by humans and only ends when they are killed.
Subverted in Eyeshield 21 numerous times, such as when Tetsuma charges at Gaou after he severely injures Kid and is still soundly defeated.
In the finale of GaoGaiGar, after the final super Zonder's (Mikoto) barrier is weakened, you would expect Guy to wrap it up and finish the fight quickly. Instead, he completely brutalizes the Zonder, ripping off one of its wings, stomping on its head, punching its arms off. To top that off, he didn't even bother with Hell and Heaven, he just aimed at the core and ripped it out. All of this while screaming in anger.
In Mobile Fighter G Gundam, this is initially played straight with Domon Kasshu's Shining Gundam and its Super Mode. He even yells "Take this! My love, my anger, and all of my sorrow!". This is later subverted as he finds out this is the "imperfect" mode. His more powerful Hyper Mode can only be used when he is in a completely zen state of peace, calm, and focus.
See Mobile Suit Gundam SEED. See Kira get angry. See Kira go crazy, and completely disable all of his enemies in seconds.
That's not Kira angry. Go watch the episode where He and Athrun succumb to their rage and try to kill one another. Both of them convey their rage very well with the sheer brutality of their attacks. No more hesitation, no more clever tricks. Their minds are set on the same part of the dial: "Two men enter, one man leaves."
In Gundam Wing, Heero enters an Unstoppable Rage during his first use of the Gundam Epyon because of the ZERO System's side effects.
Setsuna F. Seiei from Gundam 00 generally keeps very good control of himself if he gets mad, but he does have one case of pure rage: during the intervention in Azodistan, he witnesses a scene that reminds him of the horrific war he participated in as a child, which causes him to snap and go completely ballistic on the attacking Suits. Most of the time, in Gundam 00, blind rage = quick death for pilots, be they flying a Gundam or not.
A slight variation on this would be Allelujah Haptism. Normally, he's a calm, calculated Gundam Pilot, and generally the most relaxed of the bunch (for example, he never once fought any of the Gundam Throne Units, at least not on-screen, and didn't even seem to give a damn about their activities, even when he other Gundam Pilots went to fight them. Earlier, he also endangered the entire mission just to save some civilians while HRL-backup troops arrived). However, his calm only lasts until someone else capable of using Quantum Brainwaves gets too close, especially HRL Ace Pilot Soma Peries. Then his psychotic alter ego takes over and brutally slaughters everything in sight that doesn't get away. Finally, by the end of Season 2, he learns to actually control this, which is heavily exploited during the Movie, not limited to having 2 Super Soldiers with 3 personalities in total piloting 1 mech that gets stronger because it's piloted by super soldiers.
After Decil kills Woolf Enneacle in Mobile Suit Gundam AGE, Asemu is driven to such rage that it cancels out Decil's Psychic Powers and he's unable to read Asemu's attack patterns. Decil is dead in very short order. Subverted by Flit in G1 (who only holds back because Decil was a young child at that time), and in G3 Kio subverts it after his friend Deen is killed by another Vagan because he pulls it back before actually striking the deathblow.
Fuyuki Hinata in the manga/anime Keroro Gunsou becomes so frightening when angry that all other characters shrink back in horror. It takes a very serious personal offence to rile him.
Eva-01 is going berserk against Angels multiple times to devastating effect, the most terrifying instance landing up with the Eva eating one of the angels, Shinji himself going berserk against Shamshel, and Asuka when she tears through the Mass Production Evas. In fact it's the soul of the pilot's mother inside the Eva that goes into an unstoppable rage whenever her child is in danger, and Asuka and her mom go berserk together.
In the second Rebuild of Evangelion movie, Shinji goes ballistic during his battle against Zeruel, forcibly restarting Eva-01, using his AT Field to create an artificial arm to replace the one severed from his Eva, and almost setting off Third Impact.
Ayato Kamina from RahXephon seems to be quite capable of working himself into an unstoppable rage in combat. His common method of combat is very much the raging badass screaming his way into battle, and as a general rule, the second Ayato releases a soul-tearing scream of pure rage, the enemy Dolem is about to die.
The slightly relatedEngels and Tagers get a little irritated if you knock out their pilots, and Engels become enraged if the wrong pilot gets in the cockpit. During this state, they'll try to kill anything that looks remotely threatening that isn't of the same type of being. They don't gain strength or do more damage, but they make all skill rolls as if they had three points in each skill, and don't suffer wound penalties.
Chimchar in an episode of Pokémon. That was enough for Paul to try everything he could to bring out that power again.
After being knocked unconscious by Paul's Ursaring in a later battle, the true extent of Chimchar's power is unleashed and it needs a Cooldown Hug when it doesn't go back to normal. This unnatural power has been explained as its ability, Blaze.
Later on, after it's evolved into Monferno, it does this again, and requires another Cooldown Hug from Ash in order to calm down. Then it evolves into Infernape, after which it's able to control the Ability.
In the Sinnoh League Infernape once again activates Blaze, and it looks like he's going Super Saiyan while doing it.
Also seen with the Pokemon Mankey, and more so with its evolved form Primeape, which has a Hair-Trigger Temper and goes into an Unstoppable Rage at the drop of a hat.
But none of the above hold a candle to a pissed-off Mewtwo.
Yu-Gi-Oh! naturally turned this effect into a card, "Berserker Soul", and had it used by Yami Yugi during one of his own moments of Unstoppable Rage. "DORO! MONSUTAA KAADO!"
The full story: sometime after Yugi's soul is taken by the Orichalcos, Insector Haga (Weevil Underwood) taunts Yami by tearing up a card in front of him "as a joke", claiming Yugi's soul was in it and tearing it up erased him, and Yami completely loses it. Even worse for Haga: since a duel within the Seal is effectively a Shadow Game, he physically felt each and every blow Breaker dealt to him. The true chill-down-the-spine moment, however, comes shortly after he reveals his ruse:
Yami: Wash your neck and wait, Haga.
That order was traditionally given to prisoners before being executed, meaning Yami had gone past saying "I'm going to kick your ass" and issued a death sentence to Haga, which he then proceeded to carry out with brutal efficiency.
Berserk put it in the title, so it's a major part of the series.
A particularly notable example from the anime comes during the Griffith rescue arc, when Guts finds out just what had been done to Griffith. After holding him for a few moments with tears in his eyes, he smashes through a thick wooden door to take out the bastard who had tortured him, and then proceeds to live up to the name of the series by going on a rage-fueled killing spree on every last Midland guard standing between the Hawks and the way out. They don't call this guy the "Hundred Man Slayer" for nothing.
The Berserker Armour sends the wearer into a blood-lust incapable of distinguishing between friend and foe (and slowly robs them of their senses) but in return numbs pain (which tends to lead to crippling injuries) allows full use of a person's strength (again needing weeks of recovery as a result) and fixes broken bones (by jamming the bones in question full of metal shards).
It's generally not smart to get Wolfgang Grimmer of Monster angry. It's generally not survivable either.
In Elfen Lied, the main character Lucy is almost constantly in this state when she isn't in her alternate personality Nyu, due to a lifetime of almost constant abuse, deprivation, and trauma. Considering that her powers as a diclonius are a recipe for an all-out gorefest, triggering the Lucy persona may well be the last thing you ever do.
When the Major is beating the crap out of you with a stoic expression, she's actually just toying with you until you realize the futility of trying to fight her. If you somehow manage to really make her pissed, it will be very obvious, but you will probably never get the chance to fully comprehend what's happening to you. This woman's normal range of expression consists entirely of stoic and smiling politely. When her anger is showing, the point of reasoning with her is long over. And being a cyborg, she doesn't even care if she gets limbs torn off or her body crushed, making her truly unstoppable. The only two opponents who ever defeated her were inside Humongous Mecha, which she attacked bare handed.
In Slam Dunk, the first thing Heavy Sleeper Kaede Rukawa clearly says is "My name is Rukawa Kaede, I'm a freshman, and I will never forgive whoever wakes me up when I'm napping." Cue to him beating up the gangsters who woke him up from his nap.
Several players in The Prince of Tennis have a penchant for injuring their rivals during games. The most infamous ones are Akaya Kirihara from Rikkaidai, Jin Akutsu from Yamabuki and Kippei Tachibana from Fudomine. Subverted in Tachibana's case: after he seriously injures his best friend and teammate Chitose, he becomes The Atoner and refuses to use violent tennis anymore. Which makes him easy prey for Kirihara's Devil Mode later.
Fist of the North Star: People who piss off Kenshiro (usually by going too far in their cruelty to others) usually don't live to tell the tale. In fact, if they do, they're already dead. This is at least explained in the series by the fact that his fighting style is designed to increase in power proportional to exactly how angry he is. At normal levels of anger, he can break concrete with his fists. When he is at full power, he can make a tank explode by punching the driver.
If you're an Akuma, and you tick off Allen Walker of D.Gray-Man too much, you're likely to make his Innocence upgrade. Or you might make it angry. That would be a bad thing.
Think about it in this way: a permanent upgrade to his weapon will only hamper your goals in the long run, but if you get the weapon mad you will lose so much of your force, that the scales will probably balance.
Kazuya Ryuuzaki in Daimos is generally an all around nice guy, especially towards the Earthlings, and he tries to be good for some Not So Different aliens. But after seeing Miwa's racism towards innocent aliens too many times... he snaps, jumps dodging an attempted shot from Miwa and starts beating the crap out of him using Karate (thankfully on foot, rather than stomping him with the eponymous mecha) while screaming that Miwa was actually worse than the aliens (which is actually true). Kyoshiro and Nana managed to stop him after hearing that Miwa would be arrested for his crimes, but even after being restrained, Kazuya cannot stop to scream at them telling them to stop restraining him. This also gets taken to Super Robot Wars Advance, done with full amounts of awesome.
Both Takato and Guilmon of Digimon Tamers simultaneously go into an uncharacteristic rage upon the death of Juri's Leomon, with disastrous results. Guilmon and his evolutions even have a hazard symbol to hint that you really shouldn't piss him off.
In the very final chapter of Tekkaman Blade, Blade's brain breaks down completely because of his Deadly Upgrade. Right when it looks like we're all doomed, he suddenly lets out a roar and zips off to the moon to have a nice, dramatic final battle. Did he get better? Nah. It's just that a single aspect survived the complete destruction of his entire personhood - his rage toward the Radam for taking away his family. It really puts the "unstoppable" in Unstoppable Rage.
In Chrono Crusade, Chrono has moments when his Berserk Button is pressed where he taps into his demonic power and starts to attack indiscriminately. In one particularly bad moment of this, he sets part of a city ablaze and nearly kills Rosette because of the massive drain on her soul. Which sends him into a Heroic BSOD afterwards. A major key in the events leading up to the climax is Chrono learning to control his rage.
Princess Tutu has an example of this trope, but not in with the character you'd expect. Is it Fakir, who prides himself on being the Knight? Nope. Is it Mytho, the heroic Prince from a fairytale? Not him, either. It's actually Autor — a nerdy, Drosselmeyer-obsessed scholar. When Fakir's hands are nearly cut-off by the Bookman trying to stop the story, Autor flies into a rage and defeats the axe-wielding man using only his bare hands. Not nearly as impressive as some of the other examples on this page, and it only appears briefly, but it's still surprising considering the sort of character he's portrayed as.
In Hellsing, Zorin Blitz kills Pip as he tries to carry a blinded and severely wounded Seras to safety. He requests for Seras to drink his blood so "they can defeat them together" just before he dies. Filled with intense sadness which quickly becomes rage, Seras fulfills his last wish and her true vampiric abilities awaken. She then proceeds to go batshit insane and slaughters Zorin's mooks, and finally grinds Zorin's head on the wall like a cheese grater.
Also during the Valentine Brothers attack on the Headquarters.
Alexander Anderson from the series seems to fit this trope as well when he is in combat, typically demonstrating nothing but sheer joy at the prospect of battle. He attacks Integra, a high ranking British official who didn't even want to start a fight, head on, killing her bodyguards and decapitating one of them before threatening to paint to walls with her blood. He runs into gunfire without even trying to dodge and due to his augmentations is able to slaughter hundreds of undead mooks without any difficulty. In the TV version, at one point he gets both of his arms shot off. He simply kneels to the ground and grabs his knife with his teeth, and then proceeds to run at his opponent with it while he's still being shot at. In the Manga/OVA, one of his arms still gets practically blown off, but he grips the sleeve in his teeth and keeps charging. Here, he lampshades his embodiment of the trope when he admits that, given a choice of what he could be, he would prefer to be a natural disaster. And then proves it by willingly becoming He Who Fights Monsters.
Subverted? In a Shonen anime? Unnatural! But in Shaman King, rage clouds your mind, and causes you to squander your energy. It's specifically considered something to be avoided.
Demonstrated quite well in the Yoh vs. Faust VIII fight. Faust taunts and enrages Yoh from the start of the fight by harming Manta, and when Yoh is on his last legs, his last-ditch strategy is to punch Faust's Berserk Button as hard as he can. And it probably would have worked if Yoh had had just a little more furyoku to spare.
In Gintama: Not exactly conscious rage, per se, but it is brought about by rage. In her fight against Abuto, Kagura loses all control against her Yato instinct and flies into what can be fairly called an Unstoppable Rage - though the look on her face says she's actually enjoying it in a detached, psychotic way.
Busou Renkin has a good chunk of rage, with a Victorized Kazuki duking it out with Victor. There's also Tokiko, who pumps rage through her veins instead of blood.
In Tengen Toppa Gurren Lagann Simon flies into one in the middle of taking over the Dai-Gunzan when Kamina appears to have died. He then releases so much Spiral Energy that the whole ship starts to glow, blows all the Mooks out of the ship, and he sets off a nearby volcano. It took a whalloping from Kamina to get him out of it.
Full Metal Panic!: In episode 5, Sagara and Tsubaki really piss off the school janitor, who transforms in to a chainsaw-wielding monstrosity that easily fends off their combined attacks, swallows hand grenades, and chases them around the school like puppies.
Do not anger Luffy enough to make him take off his hat. God help you if you make Luffy take off his hat. How can you do this? Insult anyone's dreams, hurt his friends, mock anything to do with a pirate's pride, threaten anyone close to him...
Luffy:You think after everything you've done to my friend, and my sea, that I'm going to let you get away with all of this?!!
To put it in perspective, the character Luffy said that to had spent over twenty years developing his plan, and it was so far along that the only way it could fail is if he happened to blab too many of his secrets to someone who would oppose it, allow that someone to discover the remaining secrets, bring that someone to his home base, and refrain from killing that someone when he had the chance. But even if a someone was armed with all that, they would need to have an absurd amount of power to stop him. And who does he do that to except for the Straw Hat Pirates? And he made it infinitely worse by kidnapping their navigator whose meteorology skills are unrivaled in that world in order to remove the only possible threat to his plan. He learned the hard way that the unpredictable cyclones of the Grand Line were nothing when compared to the Straw Hats' Unstoppable Rage.
Tell Sanji that his chivalry is naive, that he can't protect anyone, mock his status as a chef, waste food or insult a beautiful lady in his presence. For maximum effect, do all of the above at the same time.
Although this could also go under Tranquil Fury, there's also Whitebeard in the War of the Best, where after everyone witnesses Ace's death and despite sustaining heavy injuries from being shot, stabbed, slashed, burned and having half his face melted off, he defeats Akainu in 2 hits, the second hit destroying most of Marineford and separating the pirates and Marines with a giant chasm. In short, never, ever piss the old man off.
Recap of the past few Big Bads. Number 1: Arlong. Killed Nami's mother and enslaved her and her home island. Promised to free them if Nami paid him a hefty amount of money. Utilized Loophole Abuse to ensure she doesn't get the amount after eight years of hard, hard work. Mocked her and provoked her entire village to attack him in what would inevitably be a Curb-Stomp Battle with everyone she loved ending up dead. The culmination of this? Nami bursts into tears, and asks Luffy for help. He and his other three crew mates march off to Arlong Park, and a couple of hours later, Arlong is unconscious and half-dead beneath the rubble of what used to be his base, and all of his henchmen aren't much better off.
Then we have Enies Lobby. Renowned as the World Goverment's Judicial Island and one of their three centers of power, the place has 10,000 soldiers and a group of superhuman assassins to ensure that any criminals taken there are beyond all hope of saving. The assassins, CP9, forced one of the Straw Hats to join them there on penalty of having the rest of them obliterated. When the other Straw Hats found out, they defied all odds and invaded Enies Lobby. For centuries, the place stood as a stronghold, symbolizing the World Government's power and authority. In the space of a single night, the Straw Hats' invasion transformed it into a burning, ruined wasteland. Every member of CP9 was beaten, including their notorious leader. They even, apparently for the first time in history, faced down the World Government's Overkill Option, the Buster Call, and escaped! Upon encountering the aftermath, Admiral Aokiji didn't sugar-coat his assessment: they lost, badly.
Most people who made the mistake of challenging the Straw Hats provoked their Unstoppable Rage and were unable to prevent the consequences, to the point that after the Time Skip, Donquixote Doflamingo, one of the most powerful pirates in the world, The Don of the entire New World, and a guy with connections to the World Government in the highest possible places, is Genre Savvy enough to know that he needs to refrain from underestimating them.
But in the end, he's just too confident in his resources and power, and by the time he realizes that he did underestimate the Straw Hats, perhaps even more than anyone previously, they've already caused too much damage, and it doesn't take long at all before they force him to take very drastic measures…which turn out to be insufficient in any event. Even in his Chessmaster smartest, he still got outdone by the Determinator that is Luffy.
Roberta from Black Lagoon normally spends her days as a bad maid, but if you kidnap or kill her masters, she will hunt you down through single photographs and kill you. You have a slight chance of surviving if you are a member of the Green Berets, otherwise you are dead.
Shortly after Kiyomaro of Zatch Bell! comes Back from the Dead and completely wipes the floor with his opponents, one of them taunts Kiyomaro with mention of his fallen allies and receives an epic beating with epic use of Demon Head on Kiyomaro's part.
Miu gets this when she finds her friends badly beaten by Shou Kanou during the D of D arc in Historys Strongest Disciple Kenichi. How does Kenichi snap her out of it? By groping her chest. Which was apparently a technique that Ma Kensei taught him.
Bado from Dogs: Bullets & Carnage goes into Unstoppable Rage whenever he has a nicotine fit and can't find cigarettes.
When Captain Aizen appears to have been murdered, it's Hinamori who finds the body. Convinced the grinning Gin is the culprit she flies into an Unstoppable Rage, causing one of her best friends, Kira (Gin's Number Two) to step in to defend his captain. Even then, Hinamori won't stop, calm down or see reason and it takes the intervention of another captain to get the situation back under control (by arresting both Hinamori and Kira).
Edward in Fullmetal Alchemist goes into one of these when he finds that Shou Tucker, an alchemist famous for making chimeras, turned his own wife into one, and then later turned his daughter and his dog into one. Shou makes it worse however, by provoking Edward about the use of human lives, and saying that they aren't so different, leading Edward to continually scream "YOU'RE WRONG!", whilst punching him repeatedly. Ouch.
When Al sacrifices himself to give Ed his arm back, Ed goes berserk on Father Homunculus.
Al almost does this too.
Alphonse: "Mister Tucker, one more word out of you... and I'll be the one to snap."
Riza also goes into Unstoppable Rage when she thinks Lust managed to kill Mustang, and promptly empties her gun's magazine into her, reloads and repeats. Several times. Worth noting because it is a subversion rather than a straight portrayal, as when she's run out of bullets, she collapses and cries, while Lust gets back up after shrugging off the barrage without breaking a sweat.
When Mustang finally finds out that Envy killed Hughes.
Roy Mustang: "That's that... you killed Hughes..... that's all I needed to know... You don't need to say anything more, Envy. The first thing I'm gonna turn to ash is your tongue."
He makes damn good on this promise, He then proceeds to alternate between full, body-consuming explosions, and pinpoint attacks that target the most sensitive and painful areas, notably the eyes. Repeatedly. OUCH!
Notably averted, however, with the Homunculus Wrath. Despite being a ruthless fighter, he is always calm and composed in a fight.
Father as well in the Final Battle he shows much anger
Ed invokes this in his initial battle with Ling Yao's bodyguard Lan Fan. The twist is that he drives Lan Fan into an Unstoppable Rage by insulting Ling, causing her attacks to become wild and reckless, and therefore much easier to dodge and counter.
One: Do not mess with Senri's friends. Two: Do not remove Senri's eyepatch. Three: When white hair appears on his forehead (after you have ignored number two), you run away as quickly as possible, through that really isn't going to help, you're going to be clawed to bits anyway. Even if +Anima is a children's manga, it doesn't skimp on the violence when necessary.
You get to see Senri go into an Unstoppable Rage two times. Once while he is a young child, and the other time he's in Moss Mountain with Cooro, Nana, and Husky.
In the final episode of Death Note, when Light Yagami is exposed as Kira, Touta Matsuda slumps to the floorunder the weight of it all, but springs into action faster than anyone else when Light attempts to escape by murdering everyone with the Death Note piece in his watch. Matsuda then shoots him in the hand, with Manly Tears coming down as he calls Light out on leading his father (and Matsuda's Obi Wan) to slaughter for nothing. When Light tries to convince Matsuda that the only way to make Soichiro's justice worth it is to save Light and kill the SPK and investigation team, he's only more enraged, and snaps when Light once again tries to write names in the note fragment with his own blood. He shoots him multiple times, and tries to finish him off with a shot to the head, but is held back by the other members of the investigation team. Coupled with the fact that he was the only member of the team to have any doubts about whether Kira really was evil, Matsuda's Crouching Moron, Hidden Badass moment is even more impressive.
Matsuda:"I have to kill him! HE HAS TO DIE!"
Katekyo Hitman Reborn!: Averted when the berserk rage is only powerful for five minutes and it is in itself not unbeatable. Tsuna is at his best when he is on the other side, straight past normal, straight past calm, all the way onto the other side where he is completely empty of feeling and is thus at his most level of head. Results in loads of arse kicking. But... there comes the time when he just has to lose it for a moment, and that's when he kinda hit Byakuran with an X-burner so hard that Byakuran vaporized. Scary...
The otherwise peaceful and docile Ohmu of Nausicaä of the Valley of the Wind fly into an Unstoppable Rage if the Sea of Decay or any of its insects are harmed, killing and destroying everything in their path in an attempt to claim vengeance against whatever is responsible. In the manga, we're privy to their thoughts through Nausicaa's empathic link with them, and they seem to regret their actions once they regain their senses.
Nausicaa herself flies into a rage and annihilates a roomful of trained soldiers with just a staff.
The Nodos in Heroic Age are Nigh InvulnerableKaiju possessed of incredible destructive power to begin with, but under certain circumstances (such as when more than two at a time are engaged in a fight) they can go into "frenzy" (or "madness" or "mental chaos", depending on the translation), becoming even more monstrous and destructive. The Heroic Tribe apparently destroyed several entire star systems through such rages during their civil war, hence why the Golden Tribe sealed the survivors within members of other tribes, making them slaves to these "lesser" beings.
Ivan Isaac's superpower in Priest is his sheer rage and contempt for Temozarela. He doesn't even care whether or not he wins against him, he just wants Temozarela to see how angry he is.
Hajime No Ippo: Don't make Takeshi Sendo angry while in the ring. You'll live longer. Shigeta and Ippo both have been victims of his flip-outs. It's not a nice situation to be in, really.
In his fight against Bryan Hawk, Takamura goes into a state of pure, uncontrolled rage (while half-unconscious to boot) and proceeds to beat the flying shit out of Hawk.
Subverted in Soul Eater. After spending 800 years waiting, having his boss/partner killed, and going so far in his revenge plot as to grow a second, back-up body,Giriko is all sorts of insane with rage. His limitless fury gives him such a power boost that Maka and Soul are quickly on the ropes. Unfortunately, he's built up so much rage that he overloads his soul. He rages so hard his soul explodes and he dies.
Sorcerer Hunters protagonist Carrot Glace suffers a unique combination of conditions. His body naturally absorbs any spell that hits him, and the energy from that spell transforms him into some nigh-unstoppable beast. The only two people who seem consistently able to snap him out of it are his coworkers and the two girls he normally avoids whenever he can: the Misu sisters, Chocolate and Tira.
After spending almost the entire second season as nothing but a hostage, Kojuro of Sengoku Basara escapes, and finds out that Hanbe, the jerk who had constantly tried to convince him that Masamune was dead, gave his lord a scar across his back. He is less than pleased about this. He promptly rides off without a sword , finds Hanbe's unit, and proceeds to beat all of the mooks bare handed. He then steals a sword, and goes berserk on Hanbe himself.
This is also Hanbe's protege, Mitsunari's, raison d'etre. Whoever may be on the receiving end of his anger, nothing is gonna get in his way until he hunts them down and chops them into mush.
In the second series of Beyblade, Kai has a major guilt-induced Heroic BSOD while fighting Goki, because Goki's Mind-Control Eyes reminds him of Wyatt, who is dead/insane depending on the version and it was Kai's fault. ("I can't fight you. Not you.") He snaps out of it on his own, but still isn't strong enough to take down uber!Cyber Dranzer. Then Goki refers to Wyatt as "your wimpy little friend" and, well. Dranzer hits Battle Aura and the title trope ensues.
Ray follows afterwards while battling Psykick opperative Denny, who is trying to take his bit beast Drigger in an unfair 2 vs. 1 beyblade match-up, using two beyblades with the same bitbeast against him instead of just one. When their friend Zeo, an inexperienced blader tried to join in to level the playing field, he finds himself quickly outmatched and soon after his beyblade gets wrecked. When Ray sees him despondent over his ruined blade, he flies into an intense fury and wrecks Denny.
More specifically, Natsu is the poster boy for this trope in-guild. His magic operates on the principle that it becomes stronger the angrier he is, and as such is often used as a "point, shoot and win" at several arc Big Bads. This becomes darkly justified after The Reveal that he is or was an Etherious, one of Zeref's demons whose magic is fueled by feelings of anger or hate. Specifically, he's E.N.D., the mightiest of all of Zeref's demons, leader of the Dark Guild Tartaros, and created for the purpose of killing Zeref. Still a nice guy when he's not doing that though.
In Trigun, Vash is normally a pacifist who refuses to kill anyone, trying his very best to non-lethally shoot at people (unrealistic, but for the context of the story one just has to roll with it) which puts him in bad situations with the major villains of the series who don't go down as easily as a normal person would from his non-lethal shots. On one notable occasion, the villain was unaffected by Vash's attempts to non-lethally defeat him but when he murdered a lot of people right in front of Vash's eyes Vash pulls out his machine gun arm and quickly immobilizes the villain. In his weakened state, Vash knows the villain can't fight back but in his rage he seriously considers killing him. However, he holds true to his morals and lets him go. This shows you that Vash would be an unstoppable gunfighter if he went in for the kill from the start.
In the Megaman NT Warrior manga, Megaman's Super Mode starts out as this until he learns to control it. Another example comes a few chapters later when Shademan threatens Lan. Megaman rips him apart.
In Vinland Saga Canute has a divine revelation that transforms him from a frightened sissy into an incredibly charismatic and powerful leader. And the very first thing he does is to calm down a raging berserker four times the size, that is about to crush him, with a Cooldown Hug. After that, he only has to look at people to make them worship him.
In Blue Exorcist, Rin has some... problems with restraint once he draws his sword to transform into his demonic form. This was especially visible in his fight against Amaimon in the anime as he started off as a bit angrier version of himself but ended up as a snarling and growling bundle of Ax-Crazy, behaving more like a feral dog than a human. Right in front of his True Companions who up until that point thought he was a Badass Normal and definitely not the son ofSatan himself. Good thing Shiemi was on-hand for a Cooldown Hug, otherwise it would've gotten real ugly real quick.
Higurashi: When They Cry: Somewhat of a subversion in that those who perform these are usually quite unstable and sometimes presented more darkly than a standard hero, but standard procedure in most arcs nonetheless. Basically, if you harm Satoko, or don't believe in Oyashiro-sama, or if a certain Yandere thinks you're connected to her boyfriend's disappearance, you're bound to be on the receiving end of one eventually. Doesn't help that the local Hate Plague that makes people prone to dish this out in the first place seems to give them enhanced strength and senses.
Fruits Basket: BlackHaru is essentially Unstoppable Rage incarnate. Most of the time he's content to just taunt or beat up whatever poor soul rouses his ire, but when he discovers that Akito threw Rin out a second-story window, he goes into aTranquil Fury until he reaches the Sohma estate, then tries to kill Akito. It takes all of Akito's considerable powers of persuasion to stop him.
Eren Yeager, the protagonist of Attack on Titan, runs on this when he's in Titan form. It's absolutely terrifying, even to battle-hardened soldiers and fellow Titan Shifters.
Eren Yeager seems to be in a near-perpetual state of rage - the only difference when he's in Titan form is that the 'unstoppable' part finally comes into play. Most of the time when he's in human form, his anger tends to make him more of a clumsy Leeroy Jenkins than an actual threat.
In the OVA of A Choice With No Regrets, Levi, the paragon of calm and cool throughout the series, goes utterly berserk when he finds Isobel and Farlan dead, along with the Aberrant that killed them. This is not Tranquil Fury. This is pure, screaming, tearful RAGE as he completely frigging massacres the titan responsible.
Ryuko Matoi of Kill la Kill has never been the calmest girl of Honnouji Academy, but when Nui Harime pulls out the other half of the Scissor Blade Ryuko always carries and reveals herself to be the one who murdered her father, Ryuko. Goes. Fucking. BERSERK. Her rage burns so hot that Senketsu loses control due to Ryuko's blood literally boiling in her veins, resulting in Senketsu consuming her, turning her into a monstrous form.
The title character of Tiger Mask is a wrestler who survived Tiger's Cave's Training from Hell, and by them he was trained as a devastating master of fouls that scares even his fellow Tiger's Cave pupils (consider that him jumping on your teeth and dancing is not cutting loose. It doesn't even count as a foul). It takes a while to piss him off enough to cut loose, but the guys who succeeded were nearly strangled to death with his companion's attempts at helping only making things worse, nearly beaten to death (the companion of the guy above), impaled with the two halves of a broken bench (and that's after Tiger Mask broke his knee, before cutting loose), beaten almost to death with a broken back, and beaten almost to death and surviving only because Tiger Mask got back to his senses in time. Then there's the last fight in the anime... Where Tiger Mask does not recover his senses in time.