Strange things start happening to Shinichirou Asano, a second year student. A woman turns into a centipede, and he sees a girl is attacked by a monster. During all the chaos, he runs into Sakura Shimazu, who uses a bow as a weapon. She is the 37th head of the Shimazu family, tasked with ridding the world of monsters. Shinichirou and Sakuya end up fighting one of the monsters together, when Shinichirou accidentally releases one of the creatures that Sakuya captures and they cooperate to catch it.

Shinichirou tries to cheer Sakuya up after he finds out that she might lose her right to become next head of the family. The secret behind Sakuya's birth, and why she's so hung up on taking over the family becomes evident. But then a monster shows up which will test her allegiances to the past, to the present, and to herself.