Sword of the Demon Hunter

Jinta, a bodyguard to a priestess in a remote mountain village, lives during Japan's Edo period. While Jinta is an outsider to the town, he is still tasked with seeking out a demon in the forest on a quest to vanquish it. But upon meeting the demon, it instead tells Jinta of a puzzling and mysterious future. The novels' story spans 170 years from the Edo period to the Heisei period, with the protagonists traveling through space and time while seeking a meaning for why they wield the blade.