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. The twins need only one more stamp on their stamp card to earn permission to join the family's next mission. To get it, they have to pass an interview with the Yozakura Family Head, their mother Mutsumi! While that's happening, the rest of the siblings split up into teams to collect intel on Asa. Hifumi teams up with Kyoichiro and Futaba to explore one of Dr. Mozu's bases in South America!.