Romance! A crazy, overprotective brother! And...spies?!

Taiyo Asano has been on his own ever since his parents died and the only one who seems to care for him is his childhood friend and classmate, Mutsumi Yozakura. But Mutsumi has a secret-she is the head of a family of spies! And on top of that, her brother Kyoichiro is dangerously protective of her! To stop Kyoichiro from killing him, Taiyo and Mutsumi must take the ultimate leap-marriage! Because in the Yozakura family, family cannot kill family.

Hatoda, the president of the beloved yet shady toy company PoPoPPo, has transferred into Taiyo and Mutsumi's school! He challenges Taiyo to an athletics contest for a chance to shake Mutsumi's hand. Will Taiyo be able to keep this creep away from the love of his life?! Later, while out on a mission, Taiyo is intercepted by mysterious government spies from an organization called the Hinagiku-and they don't seem to want to be friends with him.