In the aftermath of the most devastating conflict mankind had ever experienced, the tiny island of Shikotan became part of the Sakhalin Oblast... and on the unhealed border in this remote corner of the world, friendship among children from two different countries timidly blossomed, striving to overcome language barriers and the waves of history. Inspired by true events.

This work depicts a "five" locked room mystery drama about two high school students, which develops in the first train in the early morning, the family restaurant after school, and the gondola of the Ferris wheel. A word that suddenly changes from everyday life to extraordinary, a psychological warfare on searching each other's minds. Youth, a fragile blue human figure, is depicted in a peculiar situation called a locked room.

In Mahoro, the fictional suburb of Tokyo, Tada works as a general problem solver for hire. One day, former classmate Gyoten appears unannounced. Both men are over 30 years old and divorced. With no explanation, Gyoten suddenly asks to spend the night at Tada's home. Eventually, Tada accepts Gyoten as his assistant and together they become involved in various cases concerning an assortment of people from different walks of life.

The murder of a young girl leaves the inhabitants of a small Japanese village in shock. The body of Emili is found by four classmates with whom she was playing. The murder is never solved. Emili's mother, Asako, is torn by grief and puts a curse on the four girls when they claim not to remember the killer's face. Each of the girls, in their own way, will do penance for their silence.

Teruo, Keigo, and Soryu, three curious elementary school children, encounter Mr. Sato, a wanted "child murderer" who has snuck into the abandoned school where they are playing to look for a time capsule.

Set within the fictional city of Mahoro, Keisuke Tada runs a "benriya" - a general problem solver for hire. His assistant is his former high school classmate Haruhiko Gyoten. A big crisis then occurs for them.