Aizawa has black hair and dark brown eyes. He is depicted as a tall man with a large afro. After the timeskip, he sports facial hair and a short crop of hair on his head.
Aizawa is an intelligent, respected member of both the NPA and Task Force. He takes his work very seriously and, for this reason, does not approve of Misa Amane's antics. He becomes annoyed when she or someone else refers to her as Misa-Misa, and he often chides Touta Matsuda for his immature behavior. Aizawa's respect for L is grudging, as Aizawa chooses to work within the law and L's methods of investigation are sometimes outside of the law. His contemptuous attitude intensifies after NPA funding for the Task Force is cut, when he conflicts with L over L's withholding of the vital fact that Watari would provide the Task Force with financial support if they chose to stay. He leaves the Task Force for a short while but returns before L's death. After Light Yagami becomes leader of the Task Force, Aizawa is the first member to suspect that Light is Kira. His lawful beliefs are exemplified when he stops Matsuda from killing Light in the final episode.
Out of all the members in the Task Force, Aizawa is the most overtly skeptical, questioning L's basis for his conclusions and expressing the most doubt in them. This is made even more clear through the fact that he seems to be the one in the Task Force who takes action against L's surveillance of Light and Misa the most, being the one responsible to end their confinement.
Aizawa has a wife named Eriko and a daughter named Yumi. Aizawa and his wife also have a baby son whose name is not revealed. Halfway through the series, it is implied that Aizawa and his wife were having marital problems as a result of Aizawa's working on-call around the clock and rarely being home. Aizawa's daughter and wife both seem to miss him, and Yumi is happy whenever he comes home. His wife Eriko, however, tends to take it in a more hostile manner. He is shown in a park, where by chance he sees his family; he begins to cry while holding his daughter. It is unknown whether he and his family were able to mend, as they are not mentioned by Aizawa after the timeskip.
Aizawa is one of the NPA officers chosen to create the Japanese Task Force with the intent of catching Kira. Aizawa is one of the few people to remain in the Task Force when the majority of the members resign, being the loudest one to demand that L show himself in person.
When L finds out that Raye Penber was the FBI agents who was tailing Kira, L installs surveillance cameras in the households of those Raye was investigating, those being the households of Soichiro Yagami and Kitamura. Aizawa is not happy with the idea, and he, along with Touta Matsuda, watches the activity of the Kitamura household during the days the cameras are being used.
When the Second Kira has Sakura TV broadcast tapes predicting the deaths of several people, Aizawa and the rest of the Task Force attempt to end the broadcast. Thanks to these attempts, Ukita is murdered, which results in Aizawa yelling at L in a fit of rage, demanding that they go to the place where Ukita was killed; however, L argues against this idea and Aizawa calms down.
When Light Yagami, L's prime suspect for being Kira, offers to have himself detained, Aizawa is convinced that Light is Kira when the killing of criminals ceased for a certain period of time while he was detained. However, when the killings resumed, Aizawa has L release Light and Misa from their confinement, thinking it's unreasonable for him to keep them detained.
When the NPA discontinues funding for the Task Force, L gives the members a choice of staying or leaving. If they stay with the Task Force, they will no longer receive a paycheck from the NPA, and because he needs to care for his family, Aizawa thinks of leaving. After Watari states that L had set aside money for the Task Force members for this kind of situation, Aizawa becomes furious. L reveals that he had not mentioned the money because he wanted to see what Aizawa would choose to do. As a result of this dispute with L, Aizawa leaves the Task Force and returns to the NPA, working alongside his closest friend Hideki Ide. When the Task Force closes in on Kyosuke Higuchi as the third Kira, Aizawa and Ide reveal that they have secretly been working behind the scenes when a group of police cars is formed to prevent Higuchi from going any further, allowing the Task Force to arrest him.
When Light's fake rules are revealed to the Task Force, Aizawa is fully convinced Light and Misa are not Kira and, along with the other members of the Task Force, has L stop investigating them. Aizawa witnesses L's death and Light becoming the second L.
Following the timeskip, Aizawa is working under Light as part of the Task Force, along with Soichiro, Matsuda, Ide, and Kanzo Mogi. Sometime after Mello manages to take the Death Note, Kira contacts the Task Force and has them take part in a plan involving them raiding the Mafia and taking the notebook back from Mello. With this plan they successfully retrieve the notebook and discover Mello's real name, but Soichiro Yagami dies as a result.
Following these events, Near informs the Task Force of the fake rules within the Death Note, which is Light's primary alibi, which manages to have Aizawa begin to have slight doubts about Light, not being able to trust the notion of the rule being fake, as that is believing in the word of Mello, the murderer of Soichiro. When Kira followers attack the SPK's building and fail, Near uses this opportunity to point out the convenient timing of the attack and further incriminate Light, causing Aizawa to doubt Light even more, with him suppressing his suspicions because of Soichiro Yagami being Light's father. However, once Near bluffs in saying that Mogi has died at the hands of Kira, which would be strong evidence against Light, Aizawa is convinced and gives Near information about the former L confining Light, among other pieces of information, while confirming Mogi is indeed alive. This action results in Near identifying Light as the second L, and thus Kira.
With Mogi and Aizawa being confident in Light being Kira, they proceed to investigate Misa's apartment but to no avail; however, they have Mogi stay behind and keep an eye on Misa. Because of Aizawa's suspicions, he becomes Light's main obstacle in the Task Force. When Light began communicating to his proxy through Kiyomi Takada under the guise that he is investigating Takada, Aizawa leaves a nail mark on the notepad and, once he notices the nail mark is gone, he is now absolutely certain Light is Kira.
He informs Near of this, but Near is not impressed with this and states he has his own plan for taking down Kira, bluntly telling Aizawa not to make any moves besides keeping an eye on L. When Near eventually puts his plan into action, Light has Aizawa carry the Task Force's Death Note during the Yellow Box warehouse meeting, and he witnesses Light's demise and downfall.
After Light dies and Near becomes the third L, Aizawa becomes the deputy director and successor to Soichiro Yagami.
In other media
Aizawa's role in the film is more or less the same as it is in the manga and anime, although some large changes were made. Aizawa doesn't suspect Light of being Kira as he does in the manga and anime, the plot point regarding Aizawa and Near is absent (Near is not in the films), and the issues with his family are primarily absent. Aizawa is portrayed by Tatsuhito Okuda.
Aizawa's role in the TV drama is much more prominent than in the movies. He, Matsuda, and Mogi work closely with Soichiro, and as in the anime, he begins to suspect Light before the others do. He and Matsuda constantly get into brief arguments with each other that are usually broken up by Mogi. Aizawa is portrayed by Tomohisa Yuge.
Aizawa is a member of the Task Force in Death Note: The Musical. After the FBI agents are killed, the Task Force is given the option to resign and they sing Change the World Reprise about their choice. Aizawa chooses to stay with the Task Force.
In the original English script, Aizawa has a solo. In the 2015 and 2017 Japanese productions, Aizawa's part is sung by Matsuda.
Obata said that he did not plan to draw Aizawa for an extended period of time, so he "began to worry" when Aizawa continued appearing "more and more." Obata felt that originally his face was not "good for a main character" so he said he decided to "gradually make him more presentable. [laughs]" and increase the volume of his hair. Obata believes that Aizawa was "easy to draw" and that it is easy for him to draw people who "act consistently." Obata said that he drew Aizawa while believing that "it would be nice if there were lots of people like him in Japan." Obata redesigned Aizawa to "look older" and "really make it feel like four years had passed since L's death."
Toward the end of Death Note, Tsugumi Ohba decided to make Aizawa the chief of the NPA because he did not want to create a new character in the final chapter. Ohba felt that Aizawa is the best person to be the NPA head because Aizawa held connections to the Japanese police and knows Near. Ohba also said that whilst the other former Kira Investigation Team members had the same qualifications, he did not want to use Mogi due to his lack of personality development, nor Ide because he was so recently re-introduced and readers knew so little about him. Then he laughingly added, "Matsuda was out of the question! Maybe after Aizawa retires? We will see if he matures..." Obata then asked Ohba: "Do we make a new manga for just Matsuda?" And Ohba replied, "Of course not. Baka [Idiot] Takeshi-san." [Note: Ohba was joking with Obata, making a reference to the phrase often used by L, Light, and Aizawa: "Baka Matsuda!" [In English dub, "Matsuda, you idiot!"]
- In the anime, certain characters take on stylized hair colors while the viewer hears their thoughts; Aizawa's color is green.
- “Would you cut it out with all this dating, kissing and Misa-Misa talk already?! This is the Kira Investigation! Stop messing around!” (Episode 17)
- “Mogi, Ide. Help me arrest Kira, Light Yagami, the mass murderer.” (Chapter 107)
- (when Matsuda attempts to approach a dying Light) “Matsuda! Stop it. What is it this time, sympathy?” (Chapter 107)
- see Chapter 101 "Inducement"