The ability to fight without any care to anything.
The ability to become a massive and unbelievably powerful individual with a desire for battle regardless of one's own physical condition. A variation of Mythical Physiology.
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.
Being a result of the Weapon X Program, James Howlett/Wolverine 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) 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.
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.
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.
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.
Gaara (Naruto) lost control over Shukaku when Yashamaru made him believe that nobody would ever love him, causing a rampage.
Obito Uchiha (Naruto) flew into a berserk rage when he saw Kakashi kill Rin, brutally slaughtering all the Kiri-nin.
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.
Whenever her partner, Lori casts the spell, Zeruk, Kolulu (Zatch Bell!) gains a fearsome transformation of which she attacks her opponents without mercy. (click to animate)
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.
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.
Nizō Okada (Gin Tama) goes completely berserk after being taken over from his fusion with Benizakura.
Jūgo (Naruto) goes into a berserk rage whenever he lets the natural energy he passively absorbs cause his body to go out of control.