"Just because I fly into a blind, homicidal rage at the drop of a helm doesn't mean I'm incapable of appreciating the finer things in life."
― Berserker (8-Bit Theater)
"A stubborn enough person can survive just about anything. Rage is a hell of an anesthetic"
― Zaeed Massani (Mass Effect)
The ability to become a massive and unbelievably powerful individual with a desire for battle regardless of one's own physical condition.
The user is able to empty oneself of all rational restraints in battle and completely immerse oneself in combat becoming a dangerous warrior for both friend and foe. The ability allows the user to ignore fatal physical damage as if it never affected them and continue fighting with a frightening level of stamina while also being unpredictable and erratic in combat, making it hard to counter them. The rareness of this power makes-up in one's opponent being super strong as it boosts the user's adrenaline and stamina to the point they are able to wear out their opponent through sheer tenacity and ferocity alone.
In some cases, user are able to go in a berserk form through sheer rage or when they are imminent danger.
The ability could be temporary due to the emotional/power overload, usually self-destructive and/or with a severe backlash at the end.
May not be able to tell friend from foe while in the berserk state, and may risk accidentally hurting or even killing allies, friends or loved ones.
While user is able to ignore the effects of injuries sustained in the berserk state, these injuries will take full effect when they come out of the state, with ugly consequences if too much damage was taken.
While this ability makes the user much more powerful and resilient, it could also make them less intelligent.
Goliaths (Borderlands series); triggered by shooting off their helmets.
Undyne (Undertale); as Undyne the undying
SCP-076-2 - "Able" (SCP Foundation)
Being a result of the Weapon X Program, James Howlett/Wolverine (Marvel Comics) possesses an indestructible exoskeleton and bone claws of pure Adamantium, making his entire body a living and a regenerative healing factor that allows to recover even from the brink of death.
Being a clone of Wolverine, Laura Kinney/X-23 (Marvel Comics) she possesses a great variety of his abilities. The most notable are her indestructible Adamantium claws that make her into a living weapon and her regenerative healing factor that allows her to keep fight despite the pain inflicted on her, making her the second best at what she does.
Saiyans, such as Goku or Vegeta (Dragon Ball), have a naturally born instinct to fight despite whatever ailments they may receive, showcasing their status as natural born fighters.
Due to her surpressed frustrations, whenever Kale (Dragon Ball Super) transforms, she becomes a nigh-unstoppable berserker attacking anyone she can direct her anger against.
In the Jinchūriki Form Version 2, Naruto (Naruto) is unable to distinguish between friend and foe and he attacks in whatever way will enable him to defeat his target.
Gaara (Naruto) lost control over Shukaku when Yashamaru made him believe that nobody would ever love him, causing a rampage.
Jūgo (Naruto) goes into a berserk rage whenever he lets the natural energy he passively absorbs cause his body to go out of control.
If Inuyasha (InuYasha) were to ever drop Tessagia in battle and his life is in danger his demon blood takes over sending him into a berserk, feral stage. He will not know friend from foe and will slaughter all that stands in his way.
Kenpachi Zaraki (Bleach) is another prime example of a berserker, as he is able to ignore fatal strikes and overcome his opponents through sheer ferocity and bloodthrist alone.
Chopper (One Piece) goes berserk when he eats three Rumble Balls within a six-hours time span. This before the time skip, before he mastered control of this form.
When Cavendish (One Piece) falls asleep, his sadistic alter ego, Hakuba begins rampaging, killing allies and enemies alike.
Charlotte Linlin (One Piece) becomes a dangerous berserker driven by her gluttony for sweets.
Kaido (One Piece) is ruthless and brutal pirate captain with a bestial hunger for war and chaos.
Nizō Okada (Gintama) goes completely berserk after being taken over from his fusion with Benizakura.
Kagura (Gintama) losing control to her Yato instincts, becoming a berserk fighter.
Kamui (Gintama) losing control to his Yato instincts, becoming a berserk fighter.
Knowing Demolt (Zatch Bell!) wouldn't cooperate because of his savage behavior, Zofis brainwashed him with his powers. But when Demolt’s bookkeeper, Roberto Vile casted the spell Girugadomu Barusuruk, Demolt was freed from Zofis’ control and returned to his berserk personality. He even turned on Vile for giving him orders.
Girufadomu Barusuruku is a forbidden spell that turns Riou (Zatch Bell!) into a giant monster. Despite its power, in this form Riou had no control of himself and will attack allies and enemies alike.
Whenever her partner, Lori casts the spell, Zeruku, Kolulu (Zatch Bell!) gains a fearsome transformation of which she attacks her opponents without mercy.
Allenby Beardsley (Mobile Fighter G Gundam) with the Berserker System activated by her handlers.
Issei Hyoudou (Highschool DxD) loses all control and becomes a berserker after activating Juggernaut Drive.
Guts (Berserk) is a rage-driven warrior who is capable of tearing apart even demonic beings and surviving punishment that would kill a lesser human many times over when he goes berserk.
Eileen Berselian (Fairy Tail) can enhance her soldiers to be mindless monsters with her "Berserker" spell.
Utsutsu Hasegawa (Pupa) losing control to his Pupa instincts after learning what his "sister" really is, becoming a berserk monster.
Asura (Asura's Wrath) has the astounding trait of being able to immerse himself in battle despite fatal injuries and dominate his opponents through sheer tenacity and wrathful endurance.
Augus (Asura's Wrath) of the Seven Deities is a true example of a berserker due his lust for battle, his inhuman drive to fight regardless of damage, and his thrill for combat against powerful opponents.
Whenever Rick Taylor (Splatterhouse series) absorbs blood from the Corrupted, he is able to enter a Berserker form that grants him all of the powers of the Terror Mask.
Saïx (Kingdom Hearts), when he absorbs enough moonlight, is filled with a powerful berserker rage.