Warning: Contains spoilers for Demon Slayer: Kimetsu no Yaiba season 2 episode 18 and the Demon Slayer manga
Who is the Upper Rank 2 demon introduced at the end of Demon Slayer: Kimetsu no Yaiba season 2? Being the strongest demons outside of Muzan, the Upper Rank Kizuki are some of the most vital antagonists in the series and the biggest roadblocks the Demon Slayers have to contest with in their fight against demons. Both the Mugen Train movie and the “Entertainment District” arc have Upper Rank Kizuki involved in their stories, and season 2 ends with the introduction of yet another one for the protagonists to eventually deal with.
After Daki and Gyutaro’s defeat, the anime shows a flashback to how the two of them became demons. As humans, Daki—originally Ume—and Gyutaro were born into poverty and forced to work as an oiran and a pimp, Gyutaro often using violence to get Ume’s money. One day, Ume stabbed a samurai client in the eye, and as retaliation, he had her burned alive. Gyutaro was severely wounded by the same samurai, and as Gyutaro desperately searched for someone to help them, a demon offered them a chance to live by becoming demons, themselves.
That demon was Doma, the Upper Rank 2 Kizuki. Interestingly enough, the Demon Slayer season 2 finale shows that he was once Upper Rank 6. Doma has been the leader of the Paradise Faith Cult since he was a human, and he uses the cult as a means of gathering humans to eat. As the Upper Rank 2 Kizuki, Doma is one of the strongest demons in the story, and he’s also very different from demons introduced both before and after him.
For starters, Doma is defined by his complete and utter apathy. Even before becoming a demon, he considered humans to be so far beneath him that they weren’t worth caring about, and while he says that he believes in the afterlife, he only does so to make fun of humans for believing in it. Beyond that, Doma is unable to express any genuine emotion, despite even regular demons in Demon Slayer: Kimetsu no Yaiba being capable of doing so, yet he’s able to easily fake them. Doma is written as a textbook sociopath, and it makes his character all the more disturbing.
Another unique aspect of Doma comes from how he has a personal connection to several of the protagonists. In the final arc of the series, it’s revealed that Doma was the one who killed Shinobu and Kanao’s sister, Kanae, and the fight against Doma in the final arc is largely Shinobu and Kanao trying to avenge her. Not only that, but Doma is also connected to Inosuke, as Inosuke’s mother was a member of Doma’s cult before she discovered his true nature as a demon and sacrificed herself to get Demon Slayer's Inosuke away from him. Aside from Muzan’s involvement with Tanjiro’s family, demons usually don’t have any personal connection to the protagonists, so Doma ends up being highly unique in that regard.
Doma stands out as a villain for how twisted and immoral he is compared to everyone else. Everyone who interacts with Doma hates him, and according to an official databook, even Muzan doesn’t like Doma. Doma won’t have an active part in the story until the final arc of Demon Slayer, but once that happens, it’ll be easy to see how much he stands out.