In a certain kingdom,
peace and public safety are protected by an order of Holy Knights.
This is the story of their captain, Holy Knight Arne.
Arne usually spends her days with her beloved Kenji while taking care of security within the kingdom.
One day, Kenji receives a request to investigate a nest of goblins. Just another run-of-the-mill request with some low-class monsters.
He accepts the request and heads out to investigate.
...That night, Arne receives terrible news. Kenji had met his end.
Unable to accept the unbearable truth, she heads out to the nest on her own to confirm it for herself.
There, she finds a powerful creature lurking where it should not be. After taking it on, she is quickly defeated, and a "Cursed Crest of Monstrous Mating" is carved into her body, marking her as its servant...
The crest transforms her body, allowing her to mate with monsters.
A terrible threat looms on the kingdom's horizon...