Rui is a major antagonist in the manga and anime series Demon Slayer: Kimetsu no Yaiba, a member of the Twelve Kizuki serving Muzan Kibutsuji, bearing the rank of Lower Rank Five, and acting as the de facto final boss of the early Natagumo Mountain arc.
Name (Human and Demon): Rui
Gender: Male
Affiliation: Twelve Kizuki (Lower Rank Five), subordinate of Muzan Kibutsuji
Race: Demon (formerly human)
Former Species: Human
Height: 135 cm
Weight: 30 kg
Hobby: Cat’s cradle (string figures)
Blood Demon Art: Threads
Residence (as a demon): Natagumo Mountain
First Appearance (anime): Episode 15
Voice Actor (anime): Koki Uchiyama
Stage Actor (stage play): Nia Akutsu
Official Popularity Poll Results:
1st Poll: 16th place (191 votes)
2nd Poll: 33rd place (236 votes)
Rui is introduced as the first currently active member of the Twelve Kizuki to appear in the story.
He commands a group of demons on Natagumo Mountain whom he forces to play the roles of his “Mother,” “Father,” “Older Brother,” and “Older Sister,” forming a twisted imitation of a family.
He is often called the “Spider Demon” due to his spider-like theme and the spider motif in his hair, as well as the spider-based abilities of his subordinates.
In the first season of the anime (Tanjiro Kamado, Unwavering Resolve Arc), Rui effectively serves as the main final boss, showcasing the terrifying gap between regular demons and the elite Twelve Kizuki.
Although he speaks softly and often appears calm, Rui quickly becomes emotional and irrational when provoked, causing his attacks to become more straightforward and easier to read.
His defining trait is an obsessive fixation on “family bonds,” which he desperately tries to recreate by controlling and terrorizing other demons.
Rui is outwardly composed and quiet, speaking in a soft, almost detached tone.
Under stress or when his idea of “family” is challenged, his calm façade shatters and he becomes furious, spiteful, and cruel.
He insists that he and his “family” are bound by unbreakable ties, but in reality he maintains control through fear, torture, and psychological abuse.
If a “family member” fails to play their role or displeases him, he punishes them harshly—burning them with sunlight, beating them, stripping them of intelligence, or reshaping their bodies.
This warped concept of “family” stems from his human memories
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