During the ancient fictional dynasty "Dayin", demons were rampant, and humans and demons were in a delicate balance.
The story mainly takes place in the fictional "Dayin Dynasty", with the imperial city where the Demon Slayer Division's headquarters is located and the border fortress "Iron Rock City" as the main scenes.
After the war between humans and demons three hundred years ago, the human race narrowly defeated the demons and established the Demon Slayer System. Nowadays, the power of the demon clan is secretly resurrected, and the Demon Slayer Department is corrupted. The protagonist accidentally obtains the ancient system and becomes a key figure in the fight against the demon clan's conspiracy.
