Aizawa, with the investigation team alias of Aihara, leaves the investigation team and remains in the police force after L gives the team members the choice to quit, but continues to assist the investigation team when necessary as a member of the police. Upon L's death, Aizawa returns to the investigation team to work under Light. Upon hearing that the 13 days rule (refer to written rules of the Death Note) is false, he begins to suspect that Light is actually Kira, and contacts Near. Aizawa passes certain information to Near that leads him to deduce Kira's real identity (i.e. Light), and Near briefly holds him at the SPK headquarters. Near agrees to release Aizawa and Mogi afterwards. In the finale, he becomes the leader of the investigation team.

Aizawa has a wife and two children; Aizawa's daughter is named Aizawa Yumi and his wife is named Aizawa Eriko.