Sakusei Miko: Kozukuri no Gi

I joined a religion where sex between a shrine maiden—a messenger of the gods—and a young man before his first intercourse is offered as a sacrifice to the gods. But now that I've lost my virginity to Miko-sama through prayer (sexual intercourse), I no longer hold any value as an offering... Just as I was worrying about that, I was chosen as the partner for Miko-sama's child-making ritual... After enduring every possible assault from the believers for a week... Finally, I engaged in serious, creampie intercourse with Miko-sama...

(Source: Fanza, translated)