Ririshiki Bushin Reiha to Amalove Nakadashi Seikatsu! ~Watashi to Ko o Nashitekure... Ongi ni wa Kono Karada de Seishin Seii Kotaeyou~

Takuma is a descendant of a noble family. One day, his grandfather tells him to infuse his pure spirit into a goddess who is under the influence of evil power. Takuma meets Reiha, who used to be a general in the Warring State Period and was reborn as a goddess. Reiha asks Takuma to purify her body, but he needs to ejaculate inside her and make a baby to purify her body.

[Edited from ErogeShop]