Most "difficult things" that visit the family are always solved by the sauna. Sakuma-kun is a laid-back bear who loves saunas more than anything. He lives on the planet called Sa-kyu, together with his slightly unique family. His father is a professor at Hokkaido Sauna University. His mother works at a snack bar. And then there's his cute little brother, Kosaku. Most "difficult things" that visit the family are always solved by the sauna. One such day, Sakuma-kun becomes aware of a family "mystery" that only he seems to notice—.