彼女の妹と秘密のステイホーム～内気娘が背徳寝取り！～

Sayoko Amafune and Aritomo Harase have started living together in preparation for their marriage.

A little while later, Sayoko's parents' house undergoes renovations, and her parents decide to move into a rented house close to their place of work.

However, Sayoko's younger sister Emiru has to live with Aritomo and Sayako for some time since Aritomo's place is near her school and her parent's place is too far away from her school.