Separation (離別, Ribetsu) is the thirty-ninth chapter of the Death Note manga series.
L's interest in Light's discovery is spurred by the fact that it appears that Kira is not just killing criminals but also businessmen. Light once suggested that if Kira was a grown man he would use his power for his own benefit rather than try to change the world. This appears to be the current case: the killing of criminals is a cover for his real agenda.
Light explains that he has been using a computer program which gave him access to police and public records, as well as those of security and intelligence services. In the past few months most of the deaths attributed to Kira have been in Japan, most of them criminals. However, Light decided to check on non-criminals who also died of heart attacks and this led him to three leading businessmen: Roppei Tamiya of the Sekimaru Corporation; Kouji Aoi of the Aoi Agency; and Takeyoshi Moriya, ex-chairman of the Yotsuba Corporation, who all died within a month of each other.
While the other companies' share prices suffered a nosedive, Yotsuba's is on the rise. Probing deeper, Light has found over a dozen deaths that have been convenient for Yotsuba and occurred since Light was first imprisoned. Some of these deaths were due to accidents, illness and even suicide. This leads Light and L to conclude that Kira can kill by more than just heart attacks.
Matsuda points out that he had a hand in this research, but Light and L appear to ignore him, more focused on the analysis.
Sometime later, the Yotsuba Kira Group holds a meeting to discuss their progress so far. The deaths of their competitors has helped increase their own stock but this has been balanced by the deaths of members of their own company. However, they do note that three deaths were by heart attacks when there should have been other causes.
Roppei Tamiya, for example, was supposed to have a fatal car accident while driving along the Japanese coast as he often did. However, his death was scheduled at a time when he was actually in Italy. Thus, since he could not die in Japan as planned, he simply died of a heart attack. Another victim was supposed to die of cancer, but since cancer takes time to develop he simply died of a heart attack. They decide to put this down to experience and not to worry (unaware of the fact that the connections have been made). They believe that the police are still focused on the deaths of criminals and, in any case, they will be dealing with the police pretty soon.
At the Kira Task Force HQ, Aizawa is updated on the latest news and agrees that it is worth pursuing. L does not believe that the original Kira is actually involved with Yotsuba since—in all "modesty"—he doubts that they'd be able to find Kira before he did. Also, even if he was found out, Kira would be more likely to kill a person rather than let them expose his real identity, let alone exploit him. It can be assumed that someone at Yotsuba has acquired Kira's powers or is in contact with someone who is.
L reveals that his associate Watari knows the financial world and can use his contacts in order to find out more about Yotsuba. They get down to work with Aizawa checking out Yotsuba's organization and Light hacking into its network. Matsuda appears to be at a loss as to what he should do.
Meanwhile Soichiro has been summoned by NPA Deputy Director Koreyoshi Kitamura. Kitamura explains that people in high places are putting on pressure to call off the Kira investigation. Kira recently killed a corrupt politician and has apparently pressured another to cancel the inquiry. He also alludes to bribes being offered. The canceling of the investigation will not be made public.
Kitamura does tell Soichiro that he and his men can continue to investigate Kira unofficially but they must also fulfill their other duties and cut off all contact with L.
Soichiro returns to the Kira investigation HQ along with Mogi, who has been at police HQ handling official Kira business such as information from the public. Matsuda tells him about the Yotsuba connection and Soichiro guesses that that is where the bribery money has come from. He also informs them of the canceling of the investigation and invites Aizawa and Matsuda to accompany him and Mogi to the NPA and resign from the police.
Soichiro warns them to think the matter out carefully. He has decided to quit but the others must consider their own careers and families. Aizawa appears especially bothered by this.
L, however, suggests that they should stay with the police. They've worked with him up until now while others dropped out, and that has already meant a lot to him. He says that he will continue alone and will one day come to police HQ with Kira's head.
The chapter's title "Separation" refers to the end of the effort sharing between the National Police Agency and the Japanese task force. Tsugumi Ohba said that he believed that he had "too much fun" with naming the previous two chapters, so he went "back into serious mode" for this chapter.