Rui

Rui is a small, short-statured boy with solid white skin marked by red dots above his eyes, beneath one eyelid, and along his right cheek. His white hair fans out like spider legs, his sclera are deep red, and his irises are white with teal lashes. The engraved characters for his rank sit in his left eye, while his right eye holds three pupils.

He wears an oversized white kimono printed with webbing on the sleeves and hem, dotted to match his face, cinched with a dark red sash. As a human he had black hair in the same spidery style and bright blue eyes, closely resembling his father.

Rui is mostly calm, detached, and oddly courteous, speaking to demons and slayers alike in measured tones, though his low voice hints at buried anger. Beneath that composure lies the cruelty common to his kind. Deeply scarred, he craves the close bonds of family yet builds his version of one entirely on terror and abuse, treating any member who fails their assigned role as worthless.

He is fiercely sensitive about family and erupts when Tanjiro calls his fabricated bonds hollow. Witnessing the genuine devotion between Tanjiro and Nezuko fixates him on claiming Nezuko as his own sister. In his final moments he recognizes that all his efforts were futile, grieves his inability to apologize to the parents he killed, and breaks down when their forgiving spirits embrace him.

As Lower Rank Five, Rui far outstrips ordinary demons, dominating the demons of Mount Natagumo and forcing them into his false family. He overwhelms Tanjiro with ease, and demons strengthened by his blood can slaughter numerous corps members. His power still falls short of the Hashira, and Giyu Tomioka decapitates him without effort. Muzan favored him highly and believed he could match a Hashira on his own.

His Blood Demon Art lets him spin extraordinarily fine, razor-sharp threads from his body and control them like a puppeteer, usually extending them from his fingertips. The threads can sever Nichirin blades and grow even deadlier when he channels blood into them. He can also share his power and appearance with other demons through his blood, regenerate rapidly, and possesses durability so great that Tanjiro cannot dent his neck with a broken sword.