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.

Searching for Mutsumi's father Momo Yozakura, Taiyo infiltrates an S.L. steamer connected to Tanpopo. For all his work, he finds no clues. The disappointing failure of a mission changes into an enchanting encounter when he meets a beautiful young woman on the train. But she is no ordinary girl--she is the White Snake, and a member of the Hazakura battalion!