The Twelve Demon Moons are divided into two groups, the Upper Moons and the Lower Moons. Each has their number engraved into their eye, with the Lower members having it in only one, whereas Upper members have it in both. This number signifies how strong the member is, with Upper Moon One being the strongest and Lower Moon Six being the weakest overall, and while the exact relationships between the two groups is unclear, it is said by Muzan himself that the Lower Moons are despised by the Upper Moons.
The Twelve Demon Moons have been given three tasks to complete by Muzan's command:
- To find the Blue Spider Lily (the key ingredient of the experimental medicine that made Muzan a demon); but since Muzan's discovery (via Hantengu [Chapter 126]) that Nezuko is sun-proof, he has decided that the Upper Moons should focus on capturing her and bring her to him.
- To destroy the Demon Slaying Corps.
- After the failure, to find the Blue Spider Lily or destroy the Demon Slaying Corps. in over a thousand years, he has decided that the demons should serve him with a suicidal devotion to insure success.
The Pillars of the Demon Slaying Corps. have killed numerous Lower Moons over the years, while the Upper Moons have killed (and eaten) numerous Pillars as proof of their strength. Since the members of the Upper Moons have not changed for over a hundred years, but at the same time the members of the Lower Moons have been killed and replaced many times over; Kibutsuji Muzan decided to dismantle the Lower Moons after the most recent failure, the death of Rui (Lower Moon 5), by summoning the remaining Lower Moons to a meeting. Muzan then proceeded to kill the unnamed 2nd, 3rd, 4th, and 6th Lower Moons after their weakness was revealed, sparing only Enmu (Lower Moon One) by giving him a chance to redeem himself by killing a pillar with an injection of his blood. But with Enmu's death by the hands Tanjirou, the Lower Moons are officially disbanded with all of their members dead.
After the deaths of Gyuutarou and Daki (Upper Moon Six), he summoned the remaining members of the Upper Moons, and gave Hantengu and Gyokko (Upper Moons 4 & 5) a mission to exterminate the Swordsmith's Village, to reduce the power of the Demon Slaying Corps. by removing their ability to fight on par with the demons without swords. Both Hantengu and Gyokko were slain, but not before Hantengu witnissed (before dying) Nezuko standing in the sun; which has changed Muzan's interest into devouring Nezuko to become perfect.
- Kokushibou (Upper Moon One)
- Douma (Upper Moon Two)
- Akaza (Upper Moon Three)
- Hantengu (Upper Moon Four, deceased)
- Gyokko (Upper Moon Five, deceased)
- Daki and Gyuutarou (Upper Moon Six, deceased)
- Enmu (Lower Moon One, deceased)
- Lower Moon Two (deceased)
- Lower Moon Three (deceased)
- Lower Moon Four (deceased)
- Rui (Lower Moon Five, deceased)
- Lower Moon Six (deceased)
- Kyogai (Formerly Lower Moon Six, deceased)