Other name: この中に1人、妹がいる！, 三人行必有我妹, 其中一个是妹妹, 其中1个是妹妹, 3人行必有我妹, My Little Sister is Among Them!, NakaImo, Who Is "IMOUTO"?
Summary: As his father's will, Shougo was transferred to an acadamy where a lot of girls attend. "while attending an acadamy find a girl that will be your partner" in other word his father's will was Shougo to make a girlfriend. However he found about that there is his little sister sepreated from birth and he doesn't even know how she look like. Then in Shougo's birthday, he recieved a cake from unknown sender, and his celephone's ring tone rings. "Happy birthday, Onii-sama. I adore you very much." it looks like his sister is also attends to this acadamy, and try to get closer to him without letting know him who she is. Can Shugo "properly" reunite with his little sister, and make a girlfriend!?