- This page is for the film series character who is L's successor. For the first film character who goes by this alias, see L. For the novel character who goes by the alias Rue Ryuzaki, see Beyond Birthday.
Ryuzaki has cheek length black hair with streaks of grey and dark grey eyes.
He usually wears a black coat, either black or gray clothing, and black boots. When he needs to conceal his face during the Kira investigation, he wears a mask. The first mask he wears is the same mask used by L, but he later gets a similar one in grey.
Ryuzaki is a skilled detective, although he initially doubts that he can live up to L. He dismisses his friends' support by saying he is just L's backup, although he later comes to embrace his role, saying that he will be better than L.
While Near and especially J are friendly with him, Ryuzaki is a bit more reserved in his friendship. He is open with them, discussing his feelings about L and the case freely. He also shows that he cares for them when he keeps them out of the case so that they won't be at risk. He gives Near some guidance in detective work, and Near tests Ryuzaki in return, such as when he begins their conversation in Japanese to prepare him for taking the Kira case even though Ryuzaki had declined to get involved before. J and Near seem to work together to encourage Ryuzaki to take the Kira case.
Ryuzaki switches easily between speaking Cantonese and Japanese. He is presumably also fluent in English, since J speaks English to him several times. It's likely that he and J grew up speaking English together at Wammy's House.
His real name is Masayuki Arai.
Ryuzaki is a member of Wammy's House, but very little is known about his past. He knows J and Near from Wammy's House, and he presumably knows Mello as well since he asks Near about him. Ryuzaki refers to himself as L's backup born from IVF, suggesting that he was created from L's DNA and raised at Wammy's House specifically to be an excellent detective like L.
Ryuzaki is fully informed on the Kira investigation and the Death Notes prior to his introduction to the series, presumably from reports that L left behind for him and the other members of Wammy's House. Before his death, L made Ryuzaki promise him that he would never use a Death Note. At some point following L's death, Ryuzaki took up the title L.
Sometime in 2015 or 2016, after the Kira murders resume, the Death Note Countermeasure Task Force attempts to contact Ryuzaki to assist them on the new Kira case, but Ryuzaki declines. In 2016, in the second episode of Death Note: New Generation, Ryuzaki goes to Hong Kong for a different case, which he solves and later discusses with Near, who informs him that the Task Force has requested his assistance again.
J contacts Ryuzaki with a new case in connection with the Death Notes. An online video depicts a girl who abruptly acts strangely, as though controlled, and it's generating attention. Ryuzaki realizes that the girl's final words are an anagram for, "Kira, I have it too." J, along with Near, convince Ryuzaki to get involved, and he flies from Hong Kong to Japan to work the case with J. He locates the girl, who killed herself as controlled by a Death Note, and messages the one who killed her, although J is unable to trace the new Kira's location. The girl's computer is hacked while Ryuzaki is in the room, and the camera turns back on, but Ryuzaki wears his mask so the other Kira is unable to see his face and he shuts down the video feed.
Afterward, Ryuzaki agrees to work with the Task Force on the investigation. J offers to assist him with the Kira investigation, but Ryuzaki rejects the offer since he does not want her to risk her life with him.
In the film Death Note: Light Up the NEW World, Ryuzaki works with Tsukuru Mishima and the Task Force and searches for the six Death Notes. He helps track down the new Death Note users, most notably Sakura Aoi and Yuki Shien. He has possession of a Death Note attached to the shinigami Arma, with whom he grows close. When Yuki Shien releases the Kira Virus, an edited recording of Light Yagami admitting he is Kira, Ryuzaki responds with an edited video of L. Within the video he encodes a secret message that he has a Death Note, which Mishima cracks.
Ryuzaki cracks the case, figuring out that the new Kira, referred to as "Neo Kira," is actually Mishima. Since Ryuzaki didn't die when Misa Amane wrote his name in her Death Note, that means his name was already written by someone else, which was Mishima. He makes Mishima touch a Death Note so he'll regain his memories. Mishima is imprisoned and the six Death Notes are secured. Ryuzaki later visits Mishima in prison on the day he is to die. Some of the Death Notes have been stolen, destroyed and need to be tracked down, and Mishima is the most capable person to do that since Ryuzaki is going to die. Ryuzaki gives Mishima his old police notebook, telling him to use only that notebook, and find the stolen Death Notes. Mishima accepts and leaves the prison, and Ryuzaki dies in the cell with his mask on.
- Ryuzaki shares many similarities with Beyond Birthday, although he is not an explicit adaptation of the character. Beyond Birthday exists in the film series separately, since the LABB murders happened in the film continuity, but the character has not explicitly been seen.
- Mishima noted that Ryuzaki is the only person who stayed "sane" after owning a Death Note.
- In the film series, Ryuzaki is the only Death Note owner who does not use his Death Note.
- Although Ryuzaki goes by the alias L, it is publicly known that he is not the original L. He is also publicly known by his alias Ryuzaki.