Sanctuary of promises and contracts~ Even if I get cuckolded~

Kuru, the chief swordsman of the kingdom, is ordered by the king to investigate the Forest of Seiko, where the altar of the god Kuseshirei is said to be. During his investigation, he meets Umi, a girl from the Kuseshi people. In order to help Kuru, who was injured during her investigation, Umi takes him to a village where the Kuseshi people live. In that village, Kuru lives with Umi and discovers what is truly important to her...