Mio Asahina and Subaru Ichijou have recently moved into the neighborhood. On the outside, the young and discreet Mio works as a florist to support her alleged grade school brother, but that is a far cry from reality. Behind this facade, the two share an incredible secret: Subaru is not a kid. When no one is around, he acts like a typical stay-at-home husband—doing the housework, cooking dinner, and waiting for his partner to return home.

A few months prior, Mio's boyfriend, Subaru, was living an ordinary life as a promising chef. However, after an inexplicable event, the young man regressed into a child before his lover's eyes. Bearing this weighty secret, Mio and Subaru confront their strange situation together as they seek answers and a way to reverse Subaru's condition.