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.

Momo left letters for each of the Yozakura siblings, detailing how they can become stronger and defeat Asa. Mutsumi decides to trust Momo’s advice. And so everyone but Mutsumi and Taiyo leaves the mansion on their training journeys, kicking off the Yozakura family’s last and biggest mission! Then, after five years have passed...