Marriage and Mutsui who became sisters and younger brothers due to their parents' remarriage in their childhood. Even as adults, they were so familiar that they would go to each other's house, but Mutsuo had a feeling that he could never confess to his sister-in-law. Meanwhile, the divorce of the parents was decided again, and the two became a relationship that could not be said to be a family or another. Mutsuo hits the thoughts he hadn't told him about his unchanging treatment as a green younger brother ...
