Ano Oni Kyoushi ga Boku no Ane ni Narun desu ka?

A young boy is initially overjoyed at the news of him having an older sister, due to his father remarrying to a woman who has a daughter. That is, until he finds out that his new sister is actually his school's strict PE teacher, Shina. With his father going off to live with his new wife, the boy will live with alone with his new sister. In their...