The Twelve Demon Moons are divided into two groups, 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 in Chapter 126) that Nezuko is sun-proof, he has decided that the Upper Moons' first focus is to capture her and bring her to him.
- The destruction of the Demon Slaying Corps.
- After over a thousand years of failing at these two tasks, Muzan has decided that Demons should serve him with suicidal devotion to ensure success.
The Pillars of the Demon Slaying Corps have killed numerous Lower Moons over the years, while the Upper Moons have killed (and eaten) many Pillars as proof of their strength. Kagaya states that its been a hundred years since an Upper Moon has been killed following the defeat of Gyutaro and Daki.  While the Lower Moons have been replaced countless times, the Upper Moons did not change over the course of 100 years. After their most recent failure with the death of Rui (Lower Moon Five), Muzan decided to dismantle the Lower Moons completely. He then proceeded to kill all of the Lower Moons, sparing only Enmu, The Lower Moon One, by giving him a chance to redeem himself by killing a Pillar. With Enmu's death by the hands of Tanjiro, the Lower Moons are functionally disbanded with all of their members dead, and with Nakime's death by the hands of Muzan himself, the Upper Moons are also functionally disbanded with all their members dead.
| Upper Moon One|
| Upper Moon Two|
| Upper Moon Three|
| Upper Moon Four|
| Former Upper|
| Upper Moon Five |
| Former Upper|
| Former Upper|
| Upper Moon Six |
| Lower Moon One |
| Lower Moon Two |
| Lower Moon Three |
| Lower Moon Four |
| Lower Moon Five |
| Lower Moon Six |
| Former Lower|
The first of the Twelve Demon Moons that was encountered in the series was the former Lower Moon Six, Kyogai, who is slain in battle by Tanjiro Kamado. Tanjiro and his companions would shortly thereafter embark on the Natagumo Mountains to face-off against Lower Moon Five, Rui, who was manipulating a group of demons to forcibly act as his family and to assist him in the killing of Demon Hunters. Tanjiro almost managed to behead Rui, but the demon outwitted him by using his threads to cut off his head. He is later saved by the timely arrival of the Water Pillar, Giyu Tomioka, who swiftly beheads Rui for good. Rui's death 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 One, Enmu.
Enmu is then given an additional injection of Muzan's blood and tasked with killing the Pillars and Tanjiro as a last chance offer to save his life, with the promise of even more blood if he were to complete his mission. Enmu later intercepted Tanjiro with his companions on a train. He planned to feast on the 200+ passengers by combining his body with the train and using his Demon Blood Technique to trap them in their dreams. 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 Three, 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 receiving word of a demon claiming its feeding ground in the Red Light District, Tengen Uzui (Sound Pillar) sets off with the aid of Tanjiro, Nezuko, Inosuke, and Zenitsu. The group manages to locate Daki and slice her neck off, only for her to reveal her older brother and the true 6th Upper Moon, Gyutaro. Gyutaro and Daki, are then revealed to be sharing bodies and were finally both defeated after their simultaneous beheading.
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 and telling Muzan. This shifted Muzan's main interest in devouring Nezuko to attain perfection.
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 fellow apprentice and brother through adoption to Zenitsu Agatsuma) became the new Upper Moon Six after an encounter with Kokushibo, thereby replacing Gyutaro and Daki. It is 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 late to save 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, nearly 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 and name as a human (Hakuji) and seeing visions of important figures of his past was he finally sedated and passed on.
Doma continues his fight against Kanao, who is unexpectedly 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.
Love Pillar, Mitsuri Kanroji and Snake Pillar, Obanai Iguro confront the newly appointed Upper Moon 4, Nakime. The demoness outwitted the pairs' attempts by the usage of her Blood Art that warps and controls the entire infrastructure of the Infinity Fortress Dimension as she sees fit. Simultaneously, the Mist Pillar, Muichiro Tokito was separated from the Rock Pillar, Gyomei Himejima by Nakime's ability, falling to the location of the highest-ranking demon, Upper Moon 1, Kokushibo.
Kokushibo instinctively sensed Muichiro because of his blood relation. Muichiro learns of his ancestral relation to Kokushibo, as well as the demon's former occupation as a Demon Slayer after an examination of his inner body. Kokushibo, impressed by Muichiro's proficiency with his Breath Style, would then unsheathe his sword revealing his Breath of The Moon forms. The attack would sever Muichiro's left arm and he is swiftly defeated with minimal effort. Instead of killing the boy, Kokushibo offers to transform Muichiro into a demon as well due to intrigue in his blood relation and fighting ability. Genya Shinazugawa would attempt to ambush Kokushibo from behind using his shotgun in an attempt to save Muichiro, but his speed proved too formidable. Genya is immediately dismantled; both arms are sliced off and he is bifurcated at his waist. Given that Kokushibo had encountered a Demon Hunter with very similar physiology about 300 years ago, he knew the way to kill him was the same way a demon is killed, decapitation. However, before Kokushibo could administer the final blow, Genya is saved by the timely arrival of his older brother and Wind Pillar, Sanemi Shinazugawa.
Sanemi manages to put up a fight against Kokushibo, albeit only for a short moment. After receiving a brutal injury from an attack, Sanemi reveals that he has "rare blood". He intended to use the intoxication of his premium blood as a distraction while fighting but to no avail. Using everything he could manage to think of and was at his wit's end; Sanemi is then almost killed by a barrage of blade swings. The pillar is saved by the intervention of his comrade, Gyomei Himejima, the Stone Pillar, the strongest Slayer in the Demon Slaying Corps.
A difficult battle ensues between the Upper Moon 1 and the pillars with the demon exploiting his extraordinary eyesight abilities along with his blades made of flesh. As he is pushed further into a corner, Kokushibo's blade grows far longer developing multiple smaller blades, further increasing both his already massive range and attack power, slowly overpowering the pillars. A weakened but still alive Genya, manages to recover and remembering Tanjiro's words that being weaker gives him the unique advantage of being unnoticed by their enemies, uses the element of surprise to shoot demon bullets into Kokushibo who is immobilized and weakened by Muichiro's blade thrust into the demon's abdomen along, the bullets growing trees inside Kokushibo, further depriving him of his movement and strength. He becomes increasingly more desperate in his desire to win, and Gyomei seizes the chances to smash his head into the ground. This does not end the Upper Moon 1 who regrows its head and hungry for victory develops flesh blades on his own body, becomes far more aggressive and monstrous. The demon, however, has an internal conflict after witnessing his ugly form through his blade's reflection, and how what he has become contrasts significantly with what he wanted to be one. As his thoughts of seeking to avoid defeat and resentment towards his self heavily conflict on him, his body begins to decay, exactly at the point where Muichiro stabbed him, struggling for a final time, the Upper Moon 1's body crumbles away, as he realizes that all he wanted was to be like his younger, more talented brother, signifying the end of the highest-ranking member of the Twelve Demon Moons.
Obanai and Mitsuri are later shown to still have great difficulties with reaching Nakime's position; constantly being thwarted in their attempts by her Blood Demon Technique throughout the entire duration of the Demon Slaying Corp's battles with the Upper Moons. The two shortly thereafter are able to reconvene with Tanjiro and Giyu with the helpful assistance of the recently slain Demoness Doctor, Tamayo's assistant, Yushiro. Yuishiro manages to ambush Nakime using his Blood Demon Technique: Blindfold while she was distracted and assumes control of her body by altering her vision. Yushiro declares his intention of vengeance against Muzan for killing Tamayo; vowing to use his Upper Moon's ability against him to disassemble the fortress and bring him to the light.