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.

Through a nutritional supplement mix-up, Kyoichiro accidentally gets shrunken down to his younger self! Will li'l Kyoichiro be better behaved? Then a new arc kicks off with the shocking arrival of the father of the Yozakura family. The sins of the past come to light as the Yozakura siblings turn their wrath on the man who betrayed them. Just what does he want, and how does Taiyo fit into his mysterious plans?