Kono Naka ni Hitori, Imouto ga Iru!

As his father's will, Shougo was transferred to an academy where a lot of girls attend. "while attending an academy 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 separated from birth and he doesn't even know how she look like. Then in Shougo's birthday, he received a cake from unknown sender, and his cellphone's ring tone rings. "Happy birthday, Onii-sama. I adore you very much." it looks like his sister is also attending this academy, and also trying to get closer to him without letting him know who she is. Can Shougo "properly" reunite with his little sister, and make a girlfriend!?