母亲再婚,与新“哥哥”夕哉一起生活——光是生活上的剧变就已经烦恼不已的神前美月,某日突然出现一名自称是幽灵的神秘少女日和,并且附身在美月身上。能让日和成佛的条件,竟然是要和她爱慕的“哥哥”相亲相爱。最过分的是被迫穿上一件奇怪的内裤,这是为什么…Mitsuki and Yuya become stepsister and stepbrother because of their parents' marriage. Mitsuki can't get along with her new family and Yuya doesn't know how to approach his new stepsister. One day, Mitsuki becomes possessed by the spirit of Hiyori. Hiyori likes Yuya and believes Yuya can help her get to heaven. Hiyori places a leather chastity belt upon on Mitsuki and a plan takes place to help send Hiyori to heaven.