The main protagonist of the Toaru Majutsu no Index series and an important character in the Toaru Kagaku no Railgun series. As a Level 0 Academy City first-year high school student, his point-of-view allows the audience to become acquainted to the mysterious world of Toaru Majutsu no Index, and is mostly involved in the events of its Magic Side.He is a typical teenager with the usual angst and laid back attitude common for his age - this is apparent in the way he handles his guardianship of Index. In spite of being her guardian, albeit unofficially, he usually leaves Index to her own devices - often unprotected and often leaves her without an explanation which causes the latter to look for him and end up being in harm's way.
He possesses the mysterious "Imagine Breaker" in his right hand, which is capable of negating all forms of magic, esper powers, and other divine abilities. This, according to Index, even includes his own good luck, as they are the blessings of God.
Because of his ability, he has been unwillingly dragged into a war between the several factions most notably between the two major churches. He lacks commitment to the role he has been thrust into and often lets his emotions get the best of him. This often results in someone close to him getting hurt first before he takes a decisive action.
He has a very strong desire to aid all those who are in need even if it means putting his life on the line and will not hesitate to challenge an opponent who is several times more powerful than himself. In spite of this, and the obvious disadvantage he is at compared to his opponents, he never really bothered on learning any offensive or defensive skills and merely relied on brute strength and the ability contained in his right hand. Because of his willingness to help others unconditionally, he has attracted the affections of many characters in the series, which Himegami Aisa jokes about, stating that his life is like a dating simulation where he is bound to unlock more paths to more girls.