The most powerful demons in Demon Slayer are called the Twelve Kizuki (Demon Moons), who are further divided into six Upper Ranks and six Lower Ranks. The Lower Ranks were later all slaughtered by Muzan in disdain of their weakness, with the exception of one: Enmu.

Enmu is the Lower Rank One demon, and the primary antagonist in the Mugen Train Arc, who appears as a young man of average height with shoulder-length black hair tinged with pink, and blue eyes that have the kanji for "Lower One" etched into the irises. These neutral features, as well as a slow, drawling voice, can make Enmu's gender seem ambiguous.

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Despite that, Enmu is, in fact, male -- and one with sadistic tendencies. He is one of the few demons throughout Demon Slayer that appears totally irredeemable, because he enjoys watching the suffering of humans.

His utter devotion to Muzan was also what saved Enmu when faced with impending death. While the rest of the Lower Moons begged for their lives, or tried to save themselves from slaughter, Enmu faced Muzan with an expression of reverence. That deviation was outside of Muzan’s expectations. As a character who enjoys feeling superior, Muzan spared Enmu, and instead gave him more blood -- and another opportunity to prove himself.

Enmu took that opportunity, and his newfound power, to hatch a nefarious plot. He merged with the Mugen Train, intending to take its passengers as his victims. Most of Enmu’s skills center around his ability to manipulate dreams and reality. He can put people to sleep in his dream realm and show them beautiful, idealistic visions, or present them with the most heart-wrenching nightmares. It's that dynamic that challenges Tanjiro’s fortitude throughout the Mugen Train Arc.

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Mugen Train FIlm _ Tanjiro's Dream State _ Kamado Siblings

When Tanjiro and his companions boarded the train to investigate a series of mysterious disappearances, Enmu dragged them into a dream realm with the intent of killing them in their sleep. However, he cruelly borrowed the hands of four vulnerable children with terminal illnesses to perform that deed, luring them with the promise of an eternity of happy dreams. Tanjiro found himself in a world of peace where his family is alive and well, a reality he had long wished for, but one that he cannot regain. Despite how easy it would have been to simply lose himself in this false but idealistic world, with the assistance of Nezuko, Tanjiro forced himself back to reality.

That is the true cruelty of Enmu. He takes advantage of people’s deepest desires and regrets, and turns it against them. His utter devotion to Muzan, as well as his genuine enjoyment of human suffering, separates him from other demons.