Accelerator’s true name is unknown, as he has been referred to by his codename since childhood due to his unparalleled esper ability. As a child prodigy, his power made him feared and isolated, leading him to become cold, ruthless, and emotionally detached. Seeking to increase his power further, he was recruited into the Sisters Project, an experiment designed to push him to Level 6 by slaughtering 20,000 Misaka Clones in staged battles.

For years, Accelerator mindlessly followed orders, treating the clones as expendable test subjects, believing that reaching Level 6 would make him untouchable and end his suffering. However, his perspective changes drastically after Kamijou Touma defeats him, exposing the emptiness of his pursuit. When he later meets Last Order, a young and innocent Misaka clone, he finds himself unable to ignore her, eventually risking his life to protect her from those who sought to exploit her.

After sustaining serious brain damage, he becomes dependent on a neural device connected to the Misaka Network, a twist of fate that forces him to rely on the clones he once killed. Though he remains brutal and violent, his journey gradually shifts toward atonement and self-discovery, as he begins using his power to protect those who cannot protect themselves.

Accelerator has pale skin, white hair, and red eyes, giving him a striking and almost ghostly appearance. His thin build and frail physique contrast with his overwhelming power, making him appear deceptively fragile despite being the strongest esper in Academy City.

He is most commonly seen wearing a black-and-white striped T-shirt, dark pants, and a choker-style device around his neck, which serves as a life-support system connected to the Misaka Network. After sustaining severe brain damage, he begins using a crutch or cane to walk, further emphasizing his physical weakness compared to his immense psychic abilities.

Despite his lethargic posture and emotionless expressions, his piercing red eyes convey an intimidating presence, making it clear that he is not someone to be underestimated.

Accelerator is cynical, brutal, and emotionally detached, having spent most of his life believing in power above all else. Initially, he views morality as meaningless, considering himself a monster beyond redemption, which leads him to show no remorse in killing thousands of Misaka clones for the sake of advancing his own strength. His reputation as a merciless and unstoppable force makes him feared throughout Academy City, and he does little to disprove this image, often mocking and humiliating his enemies before annihilating them.

However, beneath his violent and nihilistic exterior, Accelerator is a deeply wounded individual who has suffered isolation, exploitation, and emotional detachment since childhood. His first defeat at the hands of Kamijou Touma shakes his worldview, forcing him to question his purpose and the meaning of strength. His true turning point comes after he meets Last Order, whose innocence and unconditional trust force him to confront his humanity. Though he initially rejects the idea of redemption, he gradually begins to protect others, even if he refuses to admit he cares.

Even after his shift towards anti-heroism, Accelerator retains his sarcastic, aggressive, and sadistic personality, often taunting his opponents before crushing them. However, his violent tendencies become more controlled, and he redirects his brutality toward enemies who harm innocent people. Though he never seeks forgiveness for his past crimes, he dedicates himself to preventing further tragedies, proving that even a former monster can choose to fight for something other than destruction.

• The Level 6 Shift and Defeat by Kamijou Touma
  Accelerator is first introduced as the primary antagonist of the Sisters Arc, acting as the experimental subject for the Level 6 Shift Project. He effortlessly kills thousands of Misaka clones, believing that power alone determines one’s worth. However, his entire ideology is shattered when he is defeated by Kamijou Touma, a supposedly powerless Level 0 who challenges his belief that strength defines one’s existence.

• Meeting Last Order and Turning Point
  Shortly after his defeat, Accelerator encounters Last Order, a young Misaka clone with an unusually bright personality. Though he initially rejects her, he is drawn into a conspiracy involving her, forcing him to protect her from those trying to use her as a pawn. In doing so, he sustains brain damage while saving her, marking his first genuine act of selflessness.

• Becoming Academy City’s Dark Hero
  Now weakened and relying on the Misaka Network to function, Accelerator begins taking on a new role as a protector, battling against various dark organizations that threaten Last Order and the clones. Though he still retains his brutal nature, he now fights with a clear purpose, slowly transitioning into Academy City’s most feared yet reliable anti-hero.

• Fighting Against the Magic Side
  Though he primarily operates within the Science Side, Accelerator eventually crosses paths with the Magic Side, engaging in battles against magicians and supernatural threats. Despite his initial skepticism toward magic, he eventually acknowledges its existence, proving that even a scientific powerhouse like him can adapt to new battlefields.