Eleven years have passed since the fierce war between humans and demons reached a truce... The era of "Human-Demon Coexistence" has arrived. During the Great War, a young man named Eita was a wielder of the sword "Shiki no To," developed as a weapon of mass destruction. He now spends his days scraping by with day labor while searching for his long-lost younger sister, Kanna. However, one day, after saving a young demon acquaintance named David from an attacking demon army, Eita is forced to bear the sin of "Demon Slayer" once again. The wandering journey of Eita, now a fugitive, and the young demon begins!