“That's so irresponsible.”
Responsibility (責任, Sekinin) is the sixty-fifth chapter of the Death Note manga series.
Light asks Near if America had anything to do with the kidnapping, and Near denies it. Light figures that only thing left to do is to track the helicopter in which one of the kidnappers got on, but then the helicopter explodes upon Mello's orders. Aizawa calls Light and tells him that the plane has landed safely, but all of the kidnappers have suddenly mysteriously died. Light checks up on his father and sister in the other helicopter, and Soichiro tells him that he feels like a failure as a police officer and wishes to quit the force. The helicopter drops them both off at the Los Angeles police headquarters where Near plans to interview them with Light monitoring the conversation.
Back in the Shinigami Realm, a Shinigami named Sidoh has lost Death Note and hasn't written a name in it for a long time. Fearing death, he has been desperately looking for it and believes Ryuk may have taken it to the Human world.
The missile is then located in the Hudson Bay, scattered into pieces two hours ago. The SPK concludes that the notebook has probably already fallen into enemy hands. Near adds that Light basically, "handed it to them on a platter." However, Near realizes that the only way to have stopped it was to have sacrificed Soichiro and Sayu, and he emphasizes with L. He tells L that he has a good idea of who was behind the kidnapping, and if he can find definite proof, he wants L to threaten to make the names and faces of the kidnappers public, making them susceptible to Kira's judgment. They’ll want to exchange the notebook back then.
Near asks Soichiro if he noticed anything strange when he was speaking to the leader of the kidnappers over the earphone. Like, if he was eating anything specific. Like a chocolate bar. Soichiro tells him that he does recall hearing a "crack" sound, and Light realizes that Near already knows who might be behind this. He is determined to work with Near, making sure that he never figures out that he's both Kira and L.
Sidoh appears to Ryuk, demanding his Death Note back. Ryuk tells him that he's not sure of exactly where it is right now. Ryuk thinks to himself that he must not tell Light about this.
Ohba said the chapter's title "Responsibility" refers to many to different elements of the chapter like when Soichiro takes responsibility for the loss of the Death Note, and also the irresponsibility of Sidoh losing his notebook. It even refers to Ryuk's responsibility for stealing the notebook that Sidoh owned.
The chapter name also refers to the line at the end of the chapter saying, "That's so irresponsible."