In a certain village that which is having no luck conceiving children, and where oni/ogres/demons are revered as deities, a rumor has begun to circulate.

"Perhaps the guardian deity needs a sacrificial offering?"

The village's shrine maiden offers to fulfill that role.
If such a sacrifice will truly save the village, then she is more than happy to give her life in exchange.

She visits a deity's mansion deep in the mountains, and is guided by a terrifying looking subordinate.
Trembling at the thought of what kind of frightening monster the deity may be... a voice calls out to her.

"Oh.. what a pleasant surprise that such a cute girl would come to my abode."

Before her sat a handsome oni/ogre/demon wearing an extravagant kimono... The Demon Deity.

The shrine maiden was to perform a dance as part of the ritual, but the deity demanded that she dance before him naked. While embarrassed, she dances just as requested... and satisfied, the deity kisses her and takes her chastity.

This is how the shrine maiden, who was supposed to be a sacrificial offering, became the demon deity's wife... and the beginning of her days drowning in pleasure as the sexually vigorous deity tries to impregnate her every single day...