Tenken

From the One Peace Books edition

The world has been annihilated and an evil bestial deity must be appeased. Saki, a young girl, trying to escape destiny, finds refuge in an unusual and rough line of work. But she has been chosen for an unthinkable role; a princess must be sacrificed to the monster Yamata-no-Orochi at the 50 year Tenken Festival. Can Manaka, the man who is in love with her, follow her into this abyss to save her from fate; only to discover the dark secret of the ceremony?

Source: Anime News Network Encyclopedia