The story begins 23 years in the past. Junichi, then a sixth-grade elementary school student, buried a handgun used in a certain incident beneath a cherry blossom tree on the school grounds together with three classmates. The four children shared this secret, each going on to live their own lives before eventually drifting apart.
Years later, Junichi becomes a detective and is assigned to investigate a murder case. During the investigation, he reunites with Makiko, one of the friends who shared that childhood secret and also his first love, now standing before him as “detective and suspect.” It is soon revealed that the weapon used in the murder is the very handgun that the four of them buried long ago.
