There are two elder sisters who commute to an identical educational institution as the protagonist Konno Kei.

The mother instinct is strong, honoka of eldest daughter who is gently with and has wrapped warmth. Though the face is a pure and innocent sect, second daughter Eri considerable naughty.

It is natural to be interested in opposite sex if it is a healthy schoolboy, Kei was one person without the exception. Under the same roof, older sisters of two are in bathrooms and shower, furthermore to defenseless in the presence if it is done until the catnap, not to considering it as opposite sex is impossible.

The desire as a man who gathers that sort of gathering place, it is found when throwing it at elder sister's undergarment, daily... to be noted. One side the elder sister doesn't looks down on strongly blaming the thing that cute younger brother did, the brother and sister relating that are nice continued.

That day, until that exceeds that line...