Mariko has divorced her husband and lives with her eldest son, Naoya, and second son, Daisuke. Perhaps it was because of the loneliness of not having a father... Naoya and Daisuke had little desire to "share" and were always fighting with each other. Although Mariko had taught her siblings to share, she actually had a physical relationship with only Naoya. However, one day, Daisuke finds out about this fact. Mariko then decides to share her other hole, her anus, with Daisuke, but...