Himekoi

A long time ago, a divine fox saved Mikazuki village from famine. In return, the fox took one of the villagers as his bride. To this day, the villagers hold a marital ceremony every year at the summer festival. The descendant of the fox and the descendant of the bride marry, and then they spend one night together. The villagers believe that this ceremony continues to protect them from disaster. It just so turns out that, this year, those two descendants are Kanata and Kuro, and, this summer, it is their turn to marry and have sex. There's one problem -- unlike Kanata, who believes in their village's customs, Kuro does not seem too keen on his fate. Kuro's apathy hurts Kanata, who always felt that he didn't quite mind, as long as he was with Kuro...
(Source: MangaPlaza)