Twelve Kizuki

The Twelve Demon Moons are a group of twelve powerful Demons under Muzan Kibutsuji's command, who have all were given a portion of his blood which have augmented their powers.

Structure
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 are unclear, it is said by Muzan himself that the Upper Moons despise the Lower Moons. When a member of the group is kicked out of the Twelve Moon Demons,Muzan slashes of the pupils where the Number signifying their rank is located,creating an "X" shaped scar on the digit, signifying that they where no longer part of the Twelve Demon Moons. An Example of this happening is Kyogai,who had already reached his "Limit" and could no longer evolve and become stronger than he already was.

The Twelve Demon Moons have been given three tasks to complete by Muzan's command:
 * 1) 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.
 * 2) To destroy the Demon Slaying Corps.
 * 3) 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 ensuring success.

The Pillars of the Demon Slaying Corps have killed numerous Lower Moons over the years, while the Upper Moons have killed (and eaten) various 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 Five), by summoning the remaining Lower Moons to a meeting. Muzan then proceeded to kill the unnamed Lower Moons Two, Three, Four, and Six 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 of Tanjirou, the Lower Moons are officially disbanded with all of their members dead.

Overview
The first of the Twelve Demon Moons that was encountered in the series was the former Lower Moon 6, Kyogai, who is slain in battle by Tanjiro Kamado. Tanjiro and his companions would shortly thereafter embark to the Natagumo Mountains to face-off against Lower Moon 5, Rui, who was manipulating a group of demons to forcibly act as family figures to himself and to also assist him with the killing of Demon Hunters. Tanjiro would almost manage to behead Rui but unfortunately, the demon outwitted the young hunter by using his threads to cut off his own head. He is later saved by the timely arrival of the Water Pillar, Giyuu Tomioka, who swiftly beheads Rui for good. Rui's destruction would later prompt Muzan Kibutsuji to lose his entire faith in the faction's ability and proceeded to dismantle the remaining Lower Moons by coldly annihilating all members except for Lower Moon 1, Enmu.

Enmu is then tasked by Muzan with killing the Pillars and Tanjiro as a last chance offer to save his life, promising to share more of his blood should he complete the mission. Enmu later intercepted Tanjiro with his companions on a train. He planned to combine his body with the train carrying over 200 passengers to use his Demon Blood Technique and trap passengers in their dreams to feast on them en masse. Through the joint effort of Tanjiro Kamado and Inosuke Hashibira, Enmu is soundly defeated, only for their short-lived victory to be interrupted by the unexpected arrival of Upper Moon 3, Akaza. Akaza would commence battle with the Flame Pillar, Kyojuro Rengoku. After a lengthy battle, Akaza would emerge victorious, claiming the life of Kyojuro.

Daki, Upper Moon 6, is the next high ranked demon encountered. After hearing words of a demon claiming its feeding ground in the Red Light District is received by the Sound Pillar, Tengen Uzui, he sets off with the aid of Tanjiro, Nezuko, Inosuke, and Zenitsu. The group manages to locate Daki and were able to slice her neck only for her to reveal her older brother and the true 6th Upper Moon, Gyutaro. Gyutaro and Daki, revealed to be sharing bodies were both finally defeated after a lengthy confrontation by beheading the siblings simultaneously.

Immediately following the deaths of Gyutaro and Daki (Upper Moon Six), Muzan summoned the remaining members of the Upper Moons and gave Hantengu and Gyokko (Upper Moons Four & Five, respectively) 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 witnessed (before dying) Nezuko standing in the sun; which has changed Muzan's interest into devouring Nezuko to become perfect.

After his attack on the Ubayashiki Manor, Muzan escaped into the Infinity Fortress thanks to Nakime. It's revealed that Nakime has replaced Hantengu as the new Upper Moon Four and that Kaigaku (a former demon slayer and apprentice brother to Zenitsu Agatsuma) became the new Upper Moon Six to replace Gyutaro and Daki, after an encounter with Kokushibo. It's still currently unknown who the new Upper Moon Five is.

Shortly after arriving in the Infinity Fortress,Shinobu Kocho would stumble upon Upper Moon 2, Doma, feasting on his female cult followers in his chamber. A single woman survived, only to be mercilessly mutilated by Doma, despite Shinobu's hasty efforts to save her. The battle commenced between the Pillar and Upper Moon. However, Shinobu's assortment of poison proved to be useless against Doma's might. The demon would then proceed to promptly defeat and absorb the Pillar, only for Kanao Tsuyuri to arrive just too short of Doma finishing her.

Zenitsu later ran into Kaigaku and had a duel to the death with his former brother, resulting in Kaigaku's death and Zenitsu almost dying. Elsewhere in the fortress Tanjiro and Tomioka are located by Akaza. Akaza proved to be a fearsome opponent and nearly accomplished killing the two. Even after having cut off his head, Akaza through sheer willpower was able to keep his body from fading. Only through memories of his previous life as the human, Hakuji, and seeing visions of important figures of his past was he finally sedated and passed on.

Meanwhile, Doma continues his fight against Kanao, who is unexpectedly later assisted by Inosuke Hashibira. He initially overwhelms the two with his ice attributed Demon Blood Techniques but was unexpectedly weakened by the lingering effects of Shinobu's wisteria flower poison after having absorbed her body. The two through their combined efforts were then able to detach Doma's head, putting an end to him.