Natsumi Kitahara of the Kitahara family has allowed her son Haruyuki to have anal sex with her, even though she knows he desires vaginal intercourse. Over time, she has begun to experience orgasm through anal sex. Meanwhile, Marina Matsumoto of the Matsumoto family has allowed her son Seiji to have vaginal sex with her, despite knowing he desires anal intercourse. Seiji has long dreamed of the day he can have anal sex with his mother. One day, Haruyuki and Seiji make a firm decision to take action. Will this decision drastically change their lives forever?