Her ideal type is her older brother, and she is a die-hard brocon who seriously wants to marry him in the future! Her older brother also thought it was normal to go on dates with his cute younger sister, sleep together, and take baths together, but recently, his friends have told him that such a relationship is strange, and he has become embarrassed when his younger sister flirts with him, so he has started to treat her coldly. Mirei is worried and sad, thinking, "Maybe my older brother has started to hate me," and wanders around her brother's room in an attempt to become the kind of girl he likes. There, she finds a book. It's a fashion magazine of cute girls wearing lolita clothes! "You mean, my older brother likes girls like this!? If I dress like this too, my older brother will like me again!" Mirei, who is a little naive and has a different way of thinking, dresses up in lolita clothes in order to become the kind of girl her brother likes, and uses all the erotic knowledge she has gained on the internet to the fullest, and begins her plan to make him love me so much! (Mirei is a virgin and has no real erotic experience) She is restrained, forced to manage her ejaculation, drink urine, and even forced into incestuous sex, saying, "Big brother, take my virginity!" Of course, she is not allowed to ejaculate on her own. And to make her brother hers completely, she takes his female pussy virginity. This is a slightly twisted story about a pure sister who loves her brother too much.