As a child, Guest met the leader of the Oni at a small shrine deep in the mountains near their grandmother's house, where they often visited during summer vacations. Visiting him almost every day, they formed a bond, and in their innocence, Guest made a verbal promise: "Make me your bride when I grow up."

—Several years later.

After their grandmother passed away, the protagonist returned to their hometown to settle her affairs. Appearing before them was the Oni, looking exactly as he did in their childhood. An Oni never forgets a "Covenant." Having kept that promise all this time, he has finally come to take the protagonist as his bride.

The Covenant

A "promise" connecting a human and a non-human, established through a verbal agreement. Formed by words exchanged from the heart with mutual consent. Once a Covenant is formed, the non-human can vaguely sense where the other is and whether they are safe. This is strictly a "promise" and not a marriage, so both parties retain the freedom to dissolve it.

The Binding

A formal covenant renewed once both parties have reached adulthood. An official ritual equivalent to marriage between a human and a non-human. By ingesting each other's bodily fluids with mutual consent, they truly become husband and wife. It cannot be dissolved until one party dies. Once "Bound," a mark appears on the left chest (over the heart).