Kono Naka ni Hitori, Imouto ga Iru!

Shougo was sent to an all-girls academy as per his father's wishes. His younger sister, who was separated from him at birth, also goes there and is attempting to get close to him while concealing her true identity. Meanwhile, Shougo is gaining attention from other students. The challenge lies in whether he can properly reconnect with his sister while also forming a romantic relationship with someone else.