It all begins with a familiar scenario when MC’s father remarries, and he suddenly gains a new stepsister. To his astonishment, she turns out to be that girl from his class, the one famous for blessed with chest department. She’s the secret crush of nearly every dude in the campus, the unofficial idol and the star of their private fantasies.
This new sister has a rather unique, and frankly shocking, perspective on her familial duties. She operates under the firm belief that it’s a sister’s responsibility to personally “take care” of her brother pent-up “frustation”. The protagonist’s constantly pursued by the very girl he’s trying to see as family, all while she’s utterly convinced she’s just being a good sister!