Rui

thumb|Rui's calm and aloof disposition. Rui was a quasi-calm, aloof, and somewhat polite individual, rarely raising his voice, and talking to anyone, demon or Demon Slayer, with a reasonable tone and vocabulary, though his low and guttural way of speaking seems to imply repressed anger and annoyance. Every time he spoke with Tanjiro Kamado during their initial duel, he remained somewhat civil in speech. Despite this stark difference in demeanor when compared to most demons, Rui still had the cruelty that his kind possessed. In actually, he was a disturbed individual who was shaped by his desire for the close bonds that a family had and his expectance for said family members to perform their assigned roles. In spite of his yearn to experience this connection, his vision of attaining one was incredibly twisted and founded on nothing but fear of him, instilled through repeated abuse on his fellow kin, which he did with unrepentant sadism. To him, family members who do not perform their roles as he expected them to (namely to protect Rui unconditionally or follow his every instruction) were worthless and as good as dead. Well aware of his great power, he was incredibly authoritarian and cruel, having no qualms about abusing others or killing members of his own "family" by stringing them up and leaving them to be burned by the sun when they go against his wishes. In addition, according to a demon that he had recruited to be his sister, another punishment for disobedience was having their intellect taken from them, a punishment likely given to his brutish and animalistic "father". Because of his strength, he tended to act almighty and confident, although this arrogance, while hardly unfounded, did not blind him to potential threats to his life, as seen when he decided to behead himself to escape Tanjiro's attack. Furthermore, he seemed to be fully aware that all his efforts to create a "family" to feel a bond have been in vain, most evident when he saw the bond between Tanjiro and Nezuko Kamado; he denounced his family and claimed that none of them have ever reached or lived to his expectations, as well as lashing out at his "sister" for simply trying to speak. Rui's unstable nature. Because of this, Rui was incredibly sensitive to the subject of family and was furious when Tanjiro pointed out the more than evident toxicity of the bonds forged between his "family". This angered him to the point that he demanded that Tanjiro retract himself and his words and threatened to kill him if he did not comply. This stance contrasted heavily with his desire to have Nezuko for himself as his sister after witnessing her selfless act of shielding Tanjiro from his threads, becoming obsessed with the idea of developing a bond with her, albeit still through fear and torture. This contrarian behavior was further evidence to Rui's delusions, mental insanity, and emotional instability. Following his close call with Tanjiro's fatal attempt to kill him and during his battle with Giyu Tomioka, Rui's collected and calm demeanour fractures, becoming visibly angry to know that Tanjiro would have killed him if he hadn't beheaded himself and denouncing the Demon Slayer Corps as a constant annoyance to his goals. His pride in his strength also faltered when he witnesses the Water Hashira destroy his strongest threads, desperately trying again before he is beheaded. thumb|Rui begging for his parents' forgiveness. Aware of the actions he performed throughout his life, Rui was haunted with the knowledge that he himself was the one to sever his bonds with his family. In death, as his life flashed before him, he conceded that everything he had done towards his one goal was futile and he lamented his inability to apologize to his parents for killing them. Resigning himself to his fate in Hell, the unexpected appearance of his parents and their acknowledgement that they would unconditionally love him and forgive him of his actions caused Rui to break down in tears, hugging them tightly and begging for their forgiveness, showing that Lower Five was simply a boy who was forced into an inconceivably harsh fate, corrupted and anguished by his failure to see a true love he once possessed.

Rui was a boy of short stature and small physical build. His skin was solid white, with red dots appearing at several spots on his face, located above his eyes where his eyebrows are supposed to be, below his left eyelid, ending above his nose, and finally a vertical one running the length of his right cheek. His hair was white and bore resemblance to spider legs. The sclera of his eyes was dark red, while his irises were white, having teal colored eyelashes. Due to holding the position of Lower Rank Five, Rui had the kanji of |Ka}} and daiji for |Go}} engraved into his left eye, signifying his ranking. His right eye on the other hand had three pupils, with one large one in the center, and two smaller ones to the right and left of the center pupil. He wore a white, oversized kimono that had spider webs etched on the sleeves and the expanse of the hem, which also possessed a loose collar, decorated with the same dot-like markings as his face, and a dark red obi belt around his waist. He also wore a plain, white juban underneath, and was barefoot. His nails bore the same color of his eyelashes. As a human, he possessed normal black hair styled with the same spider-like hairstyle, as well as bright blue eyes. He heavily resembled his human father. He wore the same white kimono, albeit without the spider web pattern, and paired it with a dull brown haori and a pair of wooden sandals. When he first transformed into a demon, both his eyes had three pupils due to not yet joining the Twelve Kizuki, and he had white eyebrows instead of the dot markings he had in the present. By the time he recruited Daughter, he looked identical to his current appearance, although he still did not have the spider web pattern on his kimono.

Overall Abilities
thumb|Rui dispatches five Demon Slayers at once with ease. As Lower Rank Five of the Twelve Kizuki, Rui was a very powerful demon. His strength and power easily surpassed that of most other demons, since he was easily able to conquer and cohere numerous demons of Mount Natagumo and force them to work for him and become members of his family. Evidence of his strength was further shown when he was able to easily overwhelm a talented fighter like Tanjiro Kamado. Furthermore, demons empowered through his blood were strong enough to kill scores of Demon Slayers easily. However, Rui's power still paled in comparison to the Hashira, having his technique easily overcome and later was effortlessly decapitated by Giyu Tomioka. Although Rui was only a demon for 20 years, he was stated to be highly capable and was well-liked by Muzan himself. It was also stated that Rui was as powerful as Lower Rank Two or One but was not obsessed with numbers and did not feel the need to enter a Blood Battle with them in order to replace them. Muzan even went as far as to expect Rui to be able to defeat a Hashira by himself despite him being a Lower Rank. It was also hinted that if Rui recovered all of the power he shared with his "family", he could have been a good match for the Hashira.