Age: 15-16
Height: 168 cm
Hair color: white
Eye color: red
Classification: Esper
Affiliation: GROUP (Former operative)
Occupation: Nagatenjouki Academy
Level: 5
Partner: Last Order
Ability: One-Way Road
Quote: "Just because I've gotten weaker, it doesn't mean that you got stronger, right?"
Theme Song: "Saikyou no Nanori"

Accelerator is the most powerful Psychic in Academy City and the main protagonist of Toaru Kagaku no Accelerator. His real name is unknown, though Accelerator recalls his surname was composed of two characters and his given name consisted of three characters. First appearing as an antagonist of the third light novel, he later becomes a main character and the lead of the science side in the Toaru Majutsu no Index series, especially in volumes 5, 8, 12, 13, SS1, SS2, 15, 14, 19, and 20.

A sadistic boy about the same age as Touma, he has an ability called "Vector Change," a form of telekinesis allowing him to change the vector values of anything he touches due in part of having a thin coat of AIM fields surrounding his body. This ability allows Accelerator perform feats such as reversing the blood flow inside a person's body, increasing the wind velocity around him to create a massive plasma storm, and blocking sound. His ability is automatic, which means that he must consciously allow gravity to affect him and that his body blocks all ultraviolet radiation, resulting his albino appearance (white hair and pale skin) because his body is unable to make melanin. The automatic nature of Redirection also prevents the use of projectiles (like bullets) and explosives (like bombs) against him.

Accelerator's unique ability made him the subject of an experiment attempting to create the first Level 6 ESPer; according to the city's best supercomputer, Tree Diagram (which was unprecedentedly destroyed by Index's Dragon Breath), this feat could only be achieved by killing 128 skilled Level 5 ESPer without a single failure. Since there are only six other known Level 5s in Academy City, an alternative plan was formed to "level up" Accelerator by having him kill 20,000 skilled Level 3 ESPers: the Misaka clones. He willingly joins the experiment to gain a reputation as the most powerful and feared ESPer that no one would be foolish enough to challenge and even killed many who got in his way.

Mikoto tries to stop the experiment to save her sisters, but it is Touma who finally does so and defeats Accelerator after discovering his weakness: Accelerator was physically weak because of his total reliance on his powers. Overconfidence in his psychic abilities resulted in his defeat as Touma beat him with his Imagine Breaker and street-fighting skills.

After his defeat in volume three of the light novels, he reappears in the fifth novel where his past was also revealed. He was taken to Academy City at a young age when his powers were first discovered but due to a lack understanding of his powers, people feared him and in some cases tried to kill him. Due to the many attempts on his life and the numerous experiments performed on him, these events shaped Accelerator into a sadist and made it hard for him to trust anyone except for Kikyou Yoshikawa, the only scientist who ever cared about him and saved his life. He also takes a more heroic role by protecting a young girl named Last Order, the last Misaka clone who believes through the memories of the Sister clones who fought him that Accelerator is not a bad person and actually never wanted to hurt the clones, trying to frighten them and telling them not to fight him, a theory Accelerator dismisses. In the aftermath of the incident, Accelerator is shot in the head by Ao Amai, damaging his brain and severely limiting the use of his power. Accelerator returns in the eighth novel with an electrode made by Heaven Canceler that links his brain with the Misaka Network. With this he is able to use half of his powers, but the battery of the electrode can only allow him to use them for 15 minutes and due to the injury he suffered, he is forced to use a cane. Toward the end of volume 13, Accelerator begins to "awaken" after nearly being killed by Amata Kihara and truly "awakens" in volume 15, gaining Black Wings, when fighting another "awakened" level 5, Teitoku Kakine, showing he no longer needs to touch in order to use his powers. In the events of the 19th novel he meets Aiwass, a higher dimensional being, summoned to their plane of existence. Aiwass explains to him when AIM entities like him are manifested, Last Order is heavily strained and may die if left untreated. To help Last Order, who has collapsed from sustaining Aiwass, Accelerator follows Aiwass' advice and heads to Russia during World War III in search of Index, unaware that he has met her before.

In Russia, after being ambushed by Russian mages, he acquires the "Goatskin," a mysterious document sought after by both Academy City and the Russian government that has the knowledge about the Archangels and Heaven, and later runs into a Misaka WORST clone, learning that Aleister intends to eliminate Last Order, now obsolete to create a new Misaka network. Despite being more powerful than the Misaka WORST clone, Accelerator is unable to bring himself to harm another clone after the Level 6 experiment and becomes mentally unstable after the clone attempts to kill Last Order and later tries to kill herself. Accelerator goes on a rampage until Touma arrives where he turns his frustration regarding Last Order's condition onto Tōma and a fight ensues between the two. After Accelerator is defeated again, Touma uses his Imagine Breaker to stabilize Last Order and leaves a note informing him of Index's true whereabouts. Later, he joins forces with Elizarinian soldiers and Misaka WORST to find spies in their country, and fought Archangel Gabriel along with Hyouka, where after studying the Goatskin, he learns to understand the angel's language turning him into an angel as a side effect. With his new powers, he is able to decode one of Index's songs and was finally able to cure Last Order but is injured in the process.

After the war of Russia ended, Accelerator made sure Academy City's Board of Directors had ordered to disband all underground factions of Academy City like GROUP, ITEM etc. With that, he finally dragged himself, and Last Order and Misaka WORST out of Academy City's dark side.

But as he was getting used to the peaceful afterwards, soon again he was caught up in the movement of GREMLIN, having to become involved with Academy City's dark side again as well as the Magic side too. He assists Levinia Birdway in the Hawaii incident, teaming up with Kamijou Touma, Misaka Mikoto and Hamazura Shiage. Later he also fights against Dark Matter Kakine Teitoku, this time teaming up with Meltdowner. Thanks to the particular fight, he finally becomes able to terms with his guilt about massacring the sisters.

In New Testament volume 7, he finds out about the Agitate Halation Project and steps into it to make sure the darkness of Academy City isn't revived because of it. It results in participating in a battle royale with a group of espers of various levels, all of whom were aiming to be the 'true hero' of the Agitate Halation project. Accelerator takes it upon himself to test the worthiness of the self proclaimed hero, saying "Interesting. Then let's put you to the test, heroes. I'll use these bloody hands to see if you are worthy of that name!!"