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

Taiyo Asano has been on his own ever since his parents died. 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!

Momo left letters for each of the Yozakura siblings, detailing how they can become stronger and defeat Asa. 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...