One day, 10-year-old Yamato and his friend Miku discover a man in a back alley whos suffering from vicious stab wounds. The man recognizes Yamato, and uses his last breath to share a secret with the children: Yamatos father was the perpetrator of a bank robbery that is known throughout the country as the most puzzling unsolved crime of the 20th century. He warns them to never trust anyone. Miku makes Yamato swear to keep the mans final words a secret. A few days later, Yamatos father is found dead, and the boy is taken in by Mikus family. The death is ruled as an accident, but Yamato has his doubts. Six years later, Yamato still cant stop wondering about the incidents, and resolves to take action.