This drama tells the story of a brother named Koto and his autistic brother Miruto, who depend on each other for survival. Koto lives a stable and trouble-free life with Miruto, who can live without any problems as long as he follows a fixed schedule. One day, a little boy who calls himself "Lion" suddenly appears beside the two of them, and they have to take him in, and the story begins. Although they are not used to it, in the process of living with the three "Lion", the brothers understand that the background of his foster care is related to "a certain incident", and from then on, the peaceful days began to be engulfed by a stormy vortex.