Quirk

Officially, the record opens with a newborn in Qing Qing City, China, whose body radiates light. Unrecorded and earlier, a prostitute carries Spearlike Bones as hardened growths along one arm and dies beside a riverbank giving birth to twins, her vitality drained away by the elder of the two before she ever grasps what she had. Once the child in China appears, similar powers surface everywhere, arriving at birth for some and at puberty for others, and the label Meta Ability sticks.

The cause was never settled. A novel illness spread by mice is one research group's theory; natural evolution running its course is another camp's; hard evidence has never propped up either. That same group publicly declares Meta holders a genetic subbranch of the species, and the announcement wrecks things. Users get branded monsters and diseased, Anti-Meta movements organize around exterminating them, criminals dubbed Villains shred civil order with their new powers, and the definition of a normal person dissolves alongside any legal consensus. Ordinary civilians fill the vacuum themselves, appearing as the first Heroes in the form of Vigilantes, until crime-fighting turns into a licensed profession beginning in Rhode Island and the Vigilantes gradually fade.

Two figures set the era's vocabulary. Zen, whom the world eventually knows as All For One, poses as a unifier by pulling abilities off people who resent them and handing them to people who want them, all while quietly gathering followers loyal to nobody but him; jealousy over the attention also drives him to murder the Luminescent Baby. Elsewhere a mother watches her son Chikara Yotsubashi absorb abuse for his ability and insists the thing is nothing more than a quirk of his. She is killed over the sentiment, yet decades afterward her word supplants Meta Ability everywhere and she is remembered as The Mother of Quirks. Chikara becomes Destro, drives the Meta Liberation Army against several nations, publishes Meta Liberation War from prison, and dies by his own hand.

Diagnosis begins, crudely, at the foot. A pinky toe holding an extra joint generally signals Quirklessness, while a single joint suggests a power is coming, the leaner skeleton being a side effect of the same evolutionary push. Manifestation typically lands before a child turns four, occasionally within days of birth, and it lands abruptly enough to startle whoever it happens to. Eijiro Kirishima's Hardening switches on at night during a trip to the toilet and cuts open his own eye. Late bloomers exist as well, which is the cover Izuku Midoriya uses to explain One For All.

Plenty of powers are not single tricks. Tsuyu Asui's Frog hands her an entire amphibian physiology, tongue and legs and camouflage together. Shoto Todoroki's Half-Cold Half-Hot reads as two separate abilities sharing one body. A rare few, Fumikage Tokoyami's Dark Shadow among them, come out sentient and talk back to their own user.

Underneath everything sits the Quirk Factor, meaning the genetic and physical apparatus a power runs through, the relevant body parts included. Kyoka Jiro's are her ears. Ruin the apparatus and the ability goes with it, which is what befalls Kai Chisaki once his arms are destroyed. A Factor lingers after death, stays detectable through a severed limb, and can be duplicated, transplanted, blended into an artificial power like the Warp Gate that Kurogiri wields, or stripped out entirely by the Quirk-Destroying Drug. Kyudai Garaki is the only person known to manage the copying.

Each power additionally carries a Vestige, the residue of a former holder's mind, which surfaces in a new owner's dreams or mindscape and occasionally fights for control. Heredity itself looks Mendelian: a child receives one parent's ability, the other parent's, or a fusion of both. Because powers behave like muscle they train up and they wear out, and overuse charges anything from dry skin to permanent scarring. Emotion feeds them, sometimes entirely, and severe enough stress triggers an Awakening that evolves an ability on the spot. Formally everything files as Emitter, Transformation or Mutant, with sub-types such as Accumulation cutting across all three.

Shoto Todoroki is the showpiece of Quirk Marriages, a practice now regarded as taboo, his ability a clean merger of Enji Todoroki's Hellflame with Rei Todoroki's Frost. His brother Toya is the counterexample. Rei's constitution gave him a tolerance for freezing temperatures and none of Enji's resistance to high heat, so his own blue flames cook him. Himiko Toga shows how far a power reaches into a personality, her fixation on blood dating to early childhood, while Manami Aiba's Love runs purely on feeling.

Holding several abilities normally reduces a person to a mindless doll incapable of speech. Izuku Midoriya, Lady Nagant, Gigantomachia and All For One are the known exceptions; Number 6, Nine and Tomura Shigaraki reach the same place only via heavy modification of body and mind. Awakenings have struck Himiko, Geten, Tomura, Katsuki Bakugo, Koji Koda, Ochaco Uraraka and Yuga Aoyama.

Two children fall outside heredity altogether. Rewind belongs to Eri, with no precedent anywhere in her bloodline; on identical terms, Darkness belongs to Koki Terumoto. Both powers are classed as variants and both get treated as especially unnatural. Her father is reverted out of existence while she is a toddler, after which her mother disowns her as a cursed child. His family reacts by having the Terumoto head demand his death over the household reputation, settling instead on locking him in a basement.

Everyone else lives under regulation. Public use breaks the law, registration with the government is mandatory, elementary schools run Quirk counseling to mixed effect, and only a licensed Pro Hero, or a student carrying a Provisional Hero License, may turn a power on a Villain. A government can classify a Hero's ability outright, which is how All Might's truth remained one of the world's great mysteries and how the New Order wielded by Star and Stripe stayed confidential. Animals qualify on rare occasion, Nezu and his High Specs standing as the usual example.