Enmu

Enmu was a member of the Twelve Demon Moons, having held the position of Lower Moon One.

Functional Recovery Training Arc
Having been summoned to a meeting of the six Lower Moons, Enmu entered the room of winding staircases with his fellow Demons. They were then confronted by a feminine-looking Kibutsuji Muzan, who demanded that they prostrate themselves, which Enmu quickly obeyed. He remained silent as his leader berated all of them for being too weak, with Muzan citing the death of Lower Moon Five, Rui, as his example.

Demon Train Arc
Enmu remained silent as Lower Moon Six was brutally killed by Muzan after being eaten alive, with almost no reaction as Lower Moon Four was subsequently slaughtered similarly to Lower Moon Six. He thought his comrade Lower Moon Three a fool as the latter panicked and attempted to flee, only to also be slain by their leader. He then listened as Lower Moon Two tried to convince Muzan of his usefulness, only for his efforts to inevitably fail to keep him alive. When asked for his final words, Enmu expresses joy at Muzan killing him personally and for the suffering of humans and his fellow Moons, thanking his leader for leaving him until last. He is then stabbed by a needle-like appendage and given some of Muzan's blood, along with the orders to kill the Demon Killing Corps' Pillars and Kamado Tanjirou. Rolling around on the floor in agony, Enmu nevertheless laughed, Muzan's promise for more blood the only thing on his mind.

Later, he stood upon the steam engine, remarking that dying while dreaming is a blessing. One of Enmu's hands spoke with the train's conductor about the success of putting the Demon Hunters to sleep and did the same to him. It then addressed the other conspirators, cautioning them about how to proceed with their plan and of its host's temporary inability to move. Back on top of the train, Enmu's main body reflected on his plan to destroy his targets' spirit cores, rendering them completely vulnerable, and of the fragile nature of human hearts. As his plan began to unfold, he noted his victims' inability to wake up and stop his twisted scheme.

Enmu then noticed that his human pawns were having trouble destroying the spirit cores, but noted that it was alright as they were simply buying time. Shortly thereafter, he turned as Kamado Tanjirou approached him, greeting him and stating that he showed him a pleasant dream, but could have made it a nightmare. Smiling, the Sleep Demon then told Tanjirou that his next dream would be of his father coming back to life.

Enmu mused over his enjoyment of first showing humans pleasant dreams and then giving them nightmares, as well as the finer details of his plan, but also wondered how Tanjirou had figured out how to wake himself so quickly. He then noticed the Demon Hunter's earrings, much to his joy, his thoughts solely on receiving more of Muzan's blood and challenging the Upper Moons with his newfound strength. An enraged Tanjirou attempted to attack the Lower Moon, but Enmu quickly put him to sleep. The youth just as quickly broke Enmu's technique, despite the Demon's multiple attempts, leading the surprised Lower Moon to compliment his determination. His neck was then severed by the furious Demon Hunter, but an unfazed Enmu merely stated that he now knew why his leader had wanted Tanjirou dead, and revealed to the shocked youth the reason for his continued survival: he had fused with the train while they had all slept. Taunting Tanjirou to protect the two hundred passengers inside of him, Enmu's severed head merged into the train.

Thanks to Tanjirou and Inosuke joint effort, they manage to discover Enmu head and subsequently, behead him.

Demon Abilities
Using his blood demon technique on an object, he can use a distance technique that upon activation will put the target in deep sleep.

Blood Demon Technique:
 * Compelling Hypnotic Whisper (のき) - A mouth forms on his hand, who tells the target to sleep and the target falls asleep.
 * Coerced Swooning Sleep: Eyeballs (・き) - Enmu creates multiple eyes on which is written "Dream" and upon looking into them, the target falls asleep.