Eri Kanzaki felt that the strangest thing he had ever encountered in his life: No one would have thought that when Eri was 14 years old, the emails he sent out of curiosity enabled him to travel back and forth between two world lines.
Eri: Fuji-kun, in order to prevent the world from being destroyed by thieves, let us save the world together!
Fuji: It seems interesting
Card! It seems a bit overdone. In short, it's a school mystery drama centered around "who stole the heroine's bat?"