With bad grades, Kyousuke is in pinch. He will have to repeat a year if he cannot pass the exam at the end of the month. When his elder sisters know about it they immediately establish the Oneechan club for the sole purpose of helping him in his studies.
Kyousuke is grateful for their support but academic assistance from his Onee-chans is not enough. He need a strong motivation. Sexual motivation that is.
Let the (sex) study begins!