The setting is an unknown land which has been protected since ancient times by "mononofu" (a pun of "mononobu" or "warriors"). These warriors have banded together to purge demons and other forces of darkness for one thousand years, thus earning their title as "demon slayers". Eight years before the main story, time and the heavens distorted and the underworld emerged into the land of man. A great demon rose from its gap and plunged the land into an age of calamity. The mononofu fought tooth and nail against the demon and its army for seven grueling days; they barely succeeded in their mission to save humanity. The great conflict was later called the "Oomagadoki", and the mononofu whom fought in it were appointed to help restore the land's political realm. The protagonist is a part of the new wave of mononofu who rise to deal with the land's never-ending demonic forces. They reside at Utakata Village, the last line of defense in the war between demons and humanity.