The year is 1590, during the turbulent Sengoku era of Japan. A girl who calls herself Izumi, the sole survivor of the destruction of her village, has come into possession of a set of very powerful keys. These keys can give their wielder access to powerful weapons that could change the course of the era.
In her flight from those who want to kill her and take them, she has washed up in a buddhist monastery, where she has met the monk Tenkai. Tenkai, who takes an interest in her troubles, may be more than he appears!