The Defense Four are detained to their homes for a week due to the events of the previous episode. Takayama receives a letter with the text "Today could be your last day." Takayama calls Sakurai for assistance. Sakurai does not answer so he instead calls Haruka. Sakurai spots Haruka on the way to meet Takayama in Akihabara. After seeing the letter, Haruka suggests the sender could be an accomplice of the bomber of the Ashio Line...