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.

To find out more information about his deceased parents, Taiyo visits the Library of the Dead. This library is infamous for its strange director, who murders anyone who makes so much as a peep in her domain! While there, he finds out that an organization known as Tanpopo was involved in his family's deaths. But the documents self-destruct while Taiyo is still inside the library--and that's way more than just a peep! Later, Taiyo and Mutsumi attempt to infiltrate a hospital known to have connections with Tanpopo, but a doctor there named Kawashita is already one step ahead of them...