The Kuranashis are a young couple who live in the lap of luxury and enjoy a comfortable wealthy lifestyle, when they suddenly have a visitor, unplanned and out of the blue.
They are informed that she is a younger half-sister by a different mother in relation to Takashi, the Kuranashi husband.
The bright, cheerful girl is invited to stay in the couple's home; however when doing so they fail to notice the dark side she has to her personality.
Sayaka prostitutes herself out for money and for pleasure, and she eventually compels Masumi to offer her own body up to men she does not know.
Sucked into a trap, she receives training, and experiences many strange excitements...

[From DLSite English]