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Villain Overview

Friends? Stop being facetious. We're not in that kind of inferior relations. In truth, we are family.
~ Rui lectures Tanjirō Kamado as he tortures his so-called "older sister" for disobeying him and not following his orders properly.

Rui Ayaki (綾木 累 Ayaki Rui), better known as Rui, is a supporting antagonist in Demon Slayer: Kimetsu no Yaiba and the main antagonist of its Natagumo Mountain Arc. He was the Lower Rank Five of the Twelve Kizuki, although it was later revealed that his true power was actually much greater. It was just that Rui was not interested in climbing up the hierarchy, which he saw as mere number-playing.

Originally a sickly child who was transformed into a demon by Muzan Kibutsuji, Rui killed his parents after they decided to kill him for harming others. Driven by guilt over the death of his parents, Rui grew to be a disturbing person and was later adopted by Muzan and became the leader of the fabricated Spider Family, made of Spider Demons that pretended to be a family.

He was voiced by Kōki Uchiyama in the Japanese version of the anime, who also voices Tomura Shigaraki in My Hero Academia, Shirou Kotomine in Fate/Apocyrpha (2017), and by Billy Kametz in the English version.


Following his parents' failure to protect him, Rui became a disturbed and childish individual who desired the close bonds that a family has and expected family members to perform their own roles. To him, "family members" who do not perform their roles as he expects them to (namely to protect him unconditionally or follow his instructions) are worthless and as good as dead.

Despite the fact he yearns for a "family", his vision of one is incredibly twisted. All he wanted was to make his fellow kin to fear him, with the fear instilled through repeated abuse on them, which he does with unrepentant sadism. He also shows no tolerance towards failure and seeks to terrify and punish whoever that failed him.

However, Rui still showed an sensitive side on his ideas of perfect family. He was clearly offended when Tanjiro called out his actions, saying Rui's family was made of naught but a fake bond and pure terror and toxicity. This stance contrasts heavily with his desire to have Nezuko for himself as his younger sister, particularly after witnessing her selfless act of shielding Tanjiro from his threads. Much to Tanjiro's shock and disgust, Rui soon became so obsessed with the idea of developing a bond with her, albeit still through fear and torture.

This contrarian behavior is a further evidence to Rui's morbid delusions, mental insanity and emotional instability. Deep down, Rui was a child who feared loneliness and desired to be loved, but his standards towards love were nothing but fear and respect with he himself as the center of his so-called "family".



Prior to his transformation into a demon, Rui was born with a weak and frail human body. This made it very difficult for him to walk and/or even breathe, causing him to spend a majority of his life trapped within his home despite cared by his parents.

Until one night, he was approached by Muzan, who offered to save him and transformed him into a demon. Rui felt great joy for having a healthy body of his own, however he had to eat humans in order to obtain sustenance. As a result, he killed a man who walked to his home, and his parents were completely horrified when they witnessed it. His father attempted to kill him, but Rui killed both of his parents in return, and went into a emotional breakdown after realizing they indeed loved them and he killed them in cold blood. However he moved on with Muzan guiding his ways.

Natagumo Mountain Arc

Following the death of his family, Rui created a fake family of his own, but tortured them, leading to the family's so-called mother wishing that she died in order to get her freedom from Rui's tyranny. Eventually, Tanjiro caught Rui torturing his so-called "sister", and called him out for it. Tanjiro then explained to Rui that terror does not make a family bond. This upsets Rui, prompting him to engage in battle in order to prove his point.

Just as Tanjiro is about to plunge his sword through Rui's neck, Rui uses his strings to destroy Tanjiro's sword, but Tanjiro ducks the super-sharp string, saving his own skin. Even with most of the blade gone, Tanjiro manages to gain the upper hand, but just before the heroic Demon Slayer can land the final blow, Rui beheads himself in order to protect his life. Recapitating himself, Rui goes in to finish his rival off, but Giyū slashes Rui's neck, at which point Lower 5 meets his end for real.


Everything is my fault. I'm sorry. I'm sorry. I'm sorry. I'm sorry!!
~ Rui wails in anguish as he begs his parents for forgiveness.

As he rots away from the blow that Giyū landed with his sword, Rui has flashbacks of when he was set to die for becoming a demon. Realising that his parents were not trying to kill him in cold blood and just wanted their child's soul to be pure, Rui apoligises to his parents for slaying them. His spirit's hair reverted back to black, and he started to doubt whether he can join them. Much to his surprise, his parents decide to accompany him to his fate in hell. At the same time, his rotting body is petted by the sympathetic Tanjiro, much to Giyū's ire.

Meanwhile, Rui's fake older sister (the one who was tortured by his webs by the time he and Tanjiro bumped into each other) continued on the run, trapping Demon Slayers in her way with web balls. She was eventually slain by Shinobu, who infected the demonic lady with Wisteria poison, which is bad for Demons.


  • Rui was ranked in 16th place as of the first character popularity poll with 191 votes.
  • He is the only Lower Rank whose demon name is the same as his human name, presumably to try to remember his human life along with a family bond.
  • Rui was the first member of the Twelve Kizuki to be confronted in the series, since Kyogai (the former Lower Rank Six) was already discarded from his duty by the time Tanjiro confronted him.
  • Rui is the only character who destroys Tanjiro's sword in battle. This happens during his duel with Tanjiro.
  • Interestingly, this wasn't the first time with Kōki Uchiyama (the voice actor of Rui) and Natsuki Hanae (the voice actor of Tanjiro) voicing two enemy characters. They already voiced Shirou Kotomine and Sieg, respectively, in Fate/Apocyrpha (2017).


           Kimetsu no Yaiba logo.svg Villains


Demon King
Muzan Kibutsuji

Twelve Demon Moons
Original Upper Moons †
One: Kokushibou † | Two: Doma † | Three: Akaza † | Four: Hantengu † | Five: Gyokko † | Six: Daki † & Gyutaro

Replacement Upper Moons †
Four: Nakime † | Six: Kaigaku

Lower Moons †
One: Enmu † | Four: Mukago † | Five: Rui † | Six: Kyogai (replaced) † Second: Hairou (past) † |

Muzan's Lesser Followers †
Susamaru and Yahaba † | Hand Demon † | Swamp Demon † | Spider FamilyFather Spider † | Mother Spider † | Brother Spider † | Sister Spider †) | Snake Demon

Tengan Uzui's Father | Iguro Family | Douma's Parents