Sei Chishiki no Nai Imouto ni, Ecchi na Massage o Shitemita Kekka...

I have a younger sister.
Her name is Kurumi...

Her body may have grown and developed nicely but...
Inside her head, she's still just a little girl.
In other words, me and Kurumi are alone together.
On a day, with no interruptions, under the guise of a "massage",
I teach her body the forbidden fruits of pleasure...

The choice of whether Kurumi ends up with a fortunate...
or misfortune future, is entirely at your fingertips...

[From DLsite English]