One

 One (一、, Ichī) is the forth chapter of Volume two and 11th chapter overall.

Plot
The investigation team finally meets L, and they are surprised by the weird, disheveled appearance of the world’s greatest detective. L tells the team to sit down and for security reasons, call him “Ryuzaki” from now on.

L shares with the investigation team his thoughts on the Kira case. He knows that Kira somehow kills his victim without contact and that Kira only needs the name of a person and their face to perform this task. Matsuda suggests that they omit crime coverage from being shown on television, but L counters the idea by pointing out that Kira is childish and hates to lose a challenge. If they omit crime coverage from the television, Kira would stoop to killing civilians. In order to psyche Kira out, L suggest that they create a fake news report revealing that the U.S. was sending 1,500 investigators to hunt for Kira. L notes that Kira is working alone and somehow has access to task force information. L has deduced that Kira was being investigated by one of the twelve FBI agents, and Kira felt threatened enough to test his powers to see if he can control people’s actions before they died. This was five days after the FBI agents arrived in Japan so Kira was being investigated during the first five days. The investigation will begin investigating the people who were being shadowed during the first five days.

Conception
The title "One" refers to several areas of the chapter; L is thinking about one clue, and Light is wondering if there is one flaw in his plan because he notices Naomi on her way to the police station to reveal one revelation that she had about the case. Also because L has become one of the members of the Japanese investigation team.