Takeshi Ninno seems to maintain a standard relationship with his stepmother, Shino Oshino, and his stepsister, Shinobu Oshino. Yet, in private, he and his stepmother are involved in a forbidden affair in which she coerces him into sexual acts. Distressed by the actions he is forced to perform, Takeshi wants to terminate the relationship, but he is also afraid that Shinobu will despise him for the intimate activities he shares with Shino. The circumstances become even more complex when his other stepsister, Fumino Oshino, unexpectedly reappears.