riko★female student, stepbrother★plain NEET man… the two of them suddenly ended up living in the same house after their parents remarried. riko is shocked by her suddenly cohabiting, unremarkable brother. during a couple's trip, riko is forced to have sex after her masturbation in her room with a vibrator she had hidden away is secretly filmed. but there was an unexpected match between the two… riko and her brother's sex compatibility was really the best. the rebellious tsundere younger sister is fucked over and over by her stepbrother she hates!