Yozakura-san Chi no Daisakusen

Follows Taiyo Asano, a boy who lost his family in a car crash. His childhood friend, Mutsumi Yozakura, is his only comfort in life. However, things change for Taiyo again, when he discovers that his teacher is not only the older brother of Mutsumi, but she also comes from a family of spies. After a fight involving the Yozakura family, Taiyo becomes Mutsumi's husband, and in order to protect her, he must become a spy himself.