Zenichiro takes advantage of Ayako's weakness and coerces her into having S&M sex every day.
But something is standing in between them. It is Ayako's younger sister and class representative, Mamiko.
Zenichiro initially disregards Mamiko, but then one night he is witness to the secret between Ayako and Mamiko.
Zenichiro can't help but chuckle under his breath...

What will become of the sisters, who are being taken advantage of by a wicked man?
Their fate rests in the hands of you, the player.

[From DLsite English]