Mofumofu de Mukomuko

Fujijiro, the fourth son of a prosperous family, aspires to become a novelist, but he is looked down by his more accomplished and prosperous brothers. Then came a marriage proposal from a distant land-owner that would give him his own property and freedom to write. But when he arrived at the village, he found that the land-owner is actually the local land-god, and Fujijiro will be offered to her as a marriage offering, as per local tradition once every 50 years!

(Source: Manga Park, translated)