Rui
Kanji
累
Rōmaji
Rui
Characteristics
Race
Demon
Human (Formerly)
Gender
Male
Age
11-13 (Physically)
>30 (Chronologically)
Affiliation
Affiliation
Twelve Kizuki
Base of Operations
Mount Natagumo
Debuts
Anime Debut
Episode 29
Manga Debut
Chapter 15
Portrayal
Japanese VA
Kōki Uchiyama
English VA
Billy Kametz
"Since I was the one with the most power, there was no one who could protect me... who could shield me. The more powerful I became, the less I remembered about being a human. And I was losing sight of what it was that I wanted to do. Seeking a bond that I could never claim for myself."
-Rui to himself in Against Corps Rules
Rui (累 Rui) was the primary antagonist in the Mount Natagumo Arc of Demon Slayer: Kimetsu no Yaiba. He was a demon affiliated with the Twelve Kizuki, holding the position of Lower Rank Five
Appearance
Rui was a young boy of short stature and a small physical build. His skin was extremely pale 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 light pink and bore resemblance to spider legs. The sclera of his eyes was red, while his irises were a pale blue. Due to holding the position of Lower Rank Five, Rui had the kanji of Lower Rank and Five engraved into his left eye, signifying his ranking of Lower Rank Five.
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. 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-leg as haircut, with bright blue eyes. He heavily resembled his human father. He wore the same white kimono but is notably plain. He paired it with a dull red haori and a pair of wooden sandals.
Personality
On a general basis, Rui was a quasi-calm and polite individual, rarely raising his voice, and talking with everyone, 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 duel he remained somewhat civil in speech, never once insulting him or calling him a name.
Rui was actually a disturbed individual who desired the close bonds that a family had and expected family members to perform their own roles. Despite the fact he yearned for a "family", his vision of 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 instructions) 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 his "family" by stringing them up and leaving them to be burned by the sun when they go against his wishes. 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 decides to behead himself to escape Tanjiro's attack.
Furthermore, he seemed to be fully aware that all his efforts to create a "family" and feel a bond have been in vain, most evident when he saw Tanjiro and Nezuko Kamado's bond; he denounces his family and claims that none of them have ever reach or lived to his expectations, as well as lashing out as his "sister" for simply trying to speak.
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, expressing silent anger 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 repel his strongest threads, desperately trying again before he is beheaded.
History
Human Life Many years ago, Rui was born to a somewhat affluent family. He had a weak, frail, and easily stressed human body; even the very act of walking and breathing was difficult for him to do, causing him to spend a majority of his life trapped within his home being cared for by his mother and father, who despite his frailty deeply loved and cherished him. He mortally wounded both of them and sat outside, reflecting on his and their actions. He recalls hearing a story about a man who drowned to save his son, and how he was moved by the act of parental love. He reasoned that because his parents tried to kill him, they must have been imposters, refusing to believe they could even think to consider killing him. Demon Life As a demon, Rui lived primarily in the forests of Mount Natagumo. Over time, he grew to become a very powerful demon, armed with both a high concentration of Muzan's blood and an extremely lethal Blood Demon Art; durable, razor-sharp threads that he could unleash at will and with great proficiency. He attained the rank of Lower Five among the Twelve Kizuki but did not care for rising up in rank. He nonetheless continued to devour humans and was said to match even Lower Two and Lower One in strength by Muzan; he subsequently saw him as a favorite among his servants. Rui lived as a demon for a little less than 20 years. One of the demons he found was a young girl, who he gave the role of being the mother of his family. Her recent transformation and human memories caused her to fall short of expectations on occasion, which he met with harsh reprimand. Mother developed an intense fear of him, even desiring death just to avoid him learning of her failure. Her "older sister" persuaded her to flee the mountain as Rui was summoned to a meeting with Muzan. As they ran into the forests, Rui found them; the demon quickly joined his side, and he subsequently killed the would-be escapee by stringing her in his threads to die in the sunlight. Mount Natagumo Arc After learning of numerous deaths on Mount Natagumo, Tanjiro Kamado and Inosuke Hashibira enter the forest to investigate, joining the Demon Slayer Murata. Rui first meets them after they learn that the Demon Slayers in the forest are being controlled by his "mother". Atop several threads, Rui appears unexpectedly and threatens the Demon Slayers, demanding they leave his "family" alone or Mother would kill them. Inosuke attempts to reach him but Rui is too far out of range. Later, as he draws a web in his hands, Rui claims that, "The five of us are going to live in bliss as a family". Later, Rui is informed by his "sister" that both their "mother" and "older brother" have been killed by the Demon Slayers. While doing so, he notices that her eyes have changed back to their original appearance. Without warning, he slashes her face with a web in his hands, causing her to fall to the ground in pain. Tanjiro, having been thrown from the battle with Father, sees the debacle and asks what Rui is doing, to which he responds that it is simply a "family matter". Angered at the blatant abuse, Tanjiro declares their familial bond fake, enraging the Lower Rank. Rui angrily demands he repeats his words but is found by another Demon Slayer. When he sees Rui as an easy kill, the demon launches a web at him, slicing the hapless Demon Slayer to pieces. Whilst Tanjiro is stunned to see his immense power, Rui demands he say his earlier statements to his face. Undaunted, Tanjiro claims their bond is forged, to Rui's fury. Rui begins to shake at the sight of her devotion to protect her siblings, causing Daughter to grow worried. He asks Tanjiro if she is his sister and realizes that even as a demon, she protected her human brother, having found the genuine sibling bond he has longed for greatly. When Daughter asks that he remember who she is and begging him not to desert her, Rui lashes out in anger, telling her to be quiet as he slices her to pieces. Infuriated, Tanjiro shouts that as long as Rui follows that mindset, he will never get what he wants. Unfazed, Rui simply asks that Tanjiro refrain from shouting, saying it's clear they don't agree. Stepping forward, Tanjiro declares he will never hand over his sister. Rui agrees, saying he will simply kill him. Tanjiro responds by saying he will simply cut of Rui's head first. Rui simply smiles in amusement, saying that is the correct spirit. He then challenges Tanjiro to try, revealing himself to be one of the Twelve Kizuki. Rui internally comments on his view of what a family should do, listing the roles of the various family members. He states that if someone doesn't understand their role, they shouldn't be alive to begin with. He then addresses Tanjiro, saying that his role is to hand over Nezuko and leave. Rui finishes by saying that noncompliance is death. Tanjiro doesn't back down, and simply looks for a path to victory. Angered, Rui shouts that Tanjiro cannot defeat him. Pulling on several threads, Rui snatches and grabs Nezuko from behind Tanjiro. He declares the matter settled but Tanjiro attacks him, nonetheless. Rui asks him if he remembers that he said he would spare Tanjiro's life if he complied. Nezuko scratches out Rui's face, but he remains passive. Rui strikes at Tanjiro, but he evades, but then notices that Nezuko is gone. When blood falls onto his sword, Rui reveals that he has strung up Nezuko and will have to discipline her, while contemplating leaving her to burn in the sunlight. Tanjiro attacks Rui once more, this time, using his Water Breathing's last form, Constant Flux. When Rui unleashes more threads, he sees that Tanjiro is now able to cut through them. Only slightly worried, he reveals his threads are not even at their maximum strength, infusing new ones with his blood. Using his Blood Demon Art, Cutting Thread Cage, Lower Five encloses the Demon Slayer in a shrinking web of enhanced threads. Seeing he is now defeated; Rui tells Tanjiro he is no longer of use and farewells him. In a moment of desperation and near death, Tanjiro, for the first time ever in battle, uses Hinokami Kagura, and is able to slice through Rui's reinforced threads using Hinokami Kagura: Dance. With his new strength, Tanjiro presses the attack, and is able to get the upper hand against Rui. Awakening, Nezuko helps her brother, unlocking her own Blood Demon Art, Exploding Blood, to burn away the threads in his path. Cornered, Rui can only watch as Tanjiro cuts through his neck with his fiery blade. As an exhausted Tanjiro tries to crawl over to Nezuko, he smells the scent of blood. Rui reveals himself to be alive, having beheaded himself to avoid Tanjiro's sword. Having had enough, Rui announces that he will simply kill Tanjiro and Nezuko, and that he hasn't been this angry in a long time. Walking over to his injured opponent, Rui wonders aloud about Nezuko's unusual power, and draws his threads. As Rui uses Blood Demon: Murderous Eye Basket to kill Tanjiro, his web is destroyed by the Water Hashira, Giyu Tomioka. In the afterlife, he laments that he will never get forgiven by his parents, going to Hell for killing others. His parents' spirits then comfort him and tell him that is not true, ensuring they will always be with him forever and they can join him. Rui begins to cry while hugging them and transforms back into his human self, asking for forgiveness as they make peace, entering the afterlife. Overall Abilities: As one of the Twelve Kizuki, Rui was one of the strongest demons in existence. This strength easily surpassed that of 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. Ultimately, Rui's power still paled in comparison to the Hashira, having his technique easily overcome and later effortlessly decapitated by Giyu Tomioka. Enhanced Durability: Rui possessed a body that was incredibly durable and hard to cut, with it easily far surpassing the hardness of lesser demons, as Tanjiro noted that Rui skin was much harder that of his "Father", who was also able to shrug off attacks from a Nichirin sword. Rui even admits that the durability of his skin far surpassed the durability of his own threads. Rui's neck is so durable that Tanjiro couldn't make a dent in it with his broken Nichirin Sword. Enhanced Strength: Rui had displayed superhuman strength, being able to easily overpower Tanjiro by simply kicking and punching him, launching him into the air or an extremely great distance seemingly effortlessly while also causing him to bleed with every blow. Menacing Aura: Rui possessed an aura that Tanjiro was noted to make the air feel thick and heavy with a mere gaze. Power Distribution: Rui possessed the ability to share his power or even his appearance with other demons if they drank his blood. The process was extremely painful for the demon, even requiring their face to be torn off to complete the transfer. Once completed, the demon will gain an appearance similar to Rui's, with pale white skin and red markings. Sometimes, they may also gain spider-like characteristics like the Elder Brother Spider Demon and Father Spider Demon. He can share his Blood Demon Art with them through a spider that they have to consume. If Rui was defeated before the rest of his "family", then the other demons that were given a portion of his power would not be able to use their Blood Demon Art he bestowed on them. Unlimited Stamina & Endurance: Like all demons, Rui possessed infinite stamina and endurance, never getting tired nor feeling pain. This was shown when he didn't flinch in the slightest when Nezuko Kamado clawed his face, causing him to bleed profusely. Rui also didn't show any signs of pain when he decapitated himself or when Giyu decapitated him. Blood Demon Art Thread Manipulation: Rui's Blood Demon Art allowed him to create thin threads indiscernible from string from his own cells and manipulate them however he pleased. He typically extended the threads from his fingertips like a puppet master. Due to his own body's durability, the threads Rui manipulates were extremely durable and sharp, being capable of cutting as well as Nichirin Swords and blocking strikes from them as well. Rui can further amplify their strength and durability by infusing his blood through them, giving them a blood red color. Techniques Cutting Thread Cage - Rui creates a web-shaped string that completely surrounds his opponent to cut them to pieces.
Murderous Eye Basket - Rui creates a spherical cage from his threads around the target, that continuously shrink until it cuts the target to pieces.
Cutting Thread Rotation - Rui creates a rotating wheel of threads, that upon reaching the opponent will cut them to pieces.
One night, Rui was approached by Muzan Kibutsuji, who then offered to "save" him and transformed him into a demon. Now possessing a strong body Rui was finally able to move about freely for the first time. However, this happiness did not last. Now a demon, Rui needed to obtain sustenance by eating humans, which then caused him to kill a man inside his home. The bloody scene was discovered by his parents, who were immediately horrified by what their son had done. Later that night, Rui awoke to his father raising a knife to kill him, while his mother sat by and sobbed.
However, as his mother lay dying, Rui overheard her apologizing for not being able to give him a healthy body, which then caused him to remember his father's last words, promising that both he and his wife would follow Rui to the afterlife by killing themselves. He came to realize that his parents did indeed love him and simply tried to stop him from fully becoming a monster, throwing Rui further into emotional turmoil. Muzan appeared shortly afterwards and told the young demon that it was his parents' fault for refusing to accept his new form. Unable to bear the weight of his actions, Rui pushed Muzan's words as the truth and believed them.
Despite being the one to sever their familial bond, Rui missed his parents dearly and spent decades trying to replicate their bond through demons. With Muzan's permission, he formed the Spider Family, locating demons found on Mount Natagumo and taking them in with the promise of protection from the Demon Slayers. Once he found them, he took them to an abandoned house he designated as his home, gave them a drop of Muzan's blood to strengthen them and altered their appearance to match his. He then assigned them with a familial role, such as the father, mother or sibling. Rui portrayed himself as the youngest son of the family, to be protected by everyone else, in spite of being the most powerful member.
Over time, various demons came to live with him and gain power. However, Rui's warped and toxic idea of a family caused conflict within much of the members. With the idea that the family must protect him as the youngest, Rui pushed high expectations on the demons and responded to failures in doing so with severe consequences.
Rui once came across a young demon as she was being pursued by several Demon Slayers. He offered her protection if she was willing to become a part of his family. When she quickly agreed to his wishes, Rui effortlessly dispatched the Demon Slayers and welcomed her in as a new sister. This demon in particular quickly found out his true views on what makes a family, his idea built on cruelty and fear.
His "family" once had at least nine members, but the number dwindled till only five remained including himself. His "parents", two siblings and the youngest son in him. On another occasion, his "mother" was tormented by her "husband'; scared, she denies knowing what made him made, only for Rui to responds that it was her fault for not knowing. Only his "father" and "older brother" were accepting of his want to have a family, while Mother and his "sister" were fearful of him.Synopsis
Rui is then seen approaching his "mother", which visibly terrifies her. He asks her on if she can truly win against the Demon Slayers. When her fear stops her from asking, he simply asks if the fight is taking to much time. He then asks that she hasten her efforts, or he will tell "Father". Mother promptly reassures Rui she will protect him, begging him not to tell Father. Rui stand for a moment, expressionless and impassive, then turns to leave, telling her to hurry up. 
Rui battles Tanjiro and uses his threads to great effect, preventing him from getting close for a potential decapitation. Tanjiro struggles greatly, as the threads are both extremely sharp and very hard to cut through. The demon offers to give him an instant death instead of a torturous one if he denies his words about his family. Despite this, Tanjiro refuses to back down, angering Rui even more at his determination. Eventually, Tanjiro tries a frontal assault but Rui is able to launch a thread directly towards him, slicing his Nichirin sword.
Though slashed across the face, Tanjiro survives by dodging sideways. Rui watches his opponent patiently as Tanjiro notes that his threads are far stronger than even Father's durable body. Lower Five continues his onslaught, launching thread after thread to prevent Tanjiro from finding a plan of attack. He asks once more if Tanjiro is willing to deny his statement, to which the Demon Slayer refuses to yield from his beliefs. With his answer, Rui unleashes webs of thread to slice him apart, only for Tanjiro's sister, Nezuko, to emerge and take the hit.
In cold anger, Rui flatly tells Daughter that none of the members of his "family" were able to perform the roles they were assigned. She claims she has become the sister he had longed for. In response to her plea for a second chance, Rui relents from further punishment and orders her to kill the remaining Demon Slayers wandering about the mountain. He says he will forgive her if she does so. Pulling herself together to heal, she agrees and leaves.
Calling out to Tanjiro, Rui says he simply wishes to talk. Tanjiro, wary, confronts him. Rui tell Tanjiro that what Nezuko did moved him. He says that Tanjiro's fate is death, but that there is a way to escape that fate. He tells Tanjiro that if Tanjiro gives him Nezuko, he will spare Tanjiro's life. When Tanjiro expresses confusion over the fact, Rui clarifies by saying that Nezuko will his little sister instead of Tanjiro's. Outraged, Tanjiro angrily tells Rui that Nezuko has her own feelings and will never be his sister. Rui, unbothered, simply says that he is stronger than Tanjiro, and will create a bond with Nezuko, that she will know exactly what happens when he is defied.
Angered, Tanjiro attacks but is quickly stopped by Rui's threads. Walking up to him, Rui kicks him, sending him a considerable distance. Rui then backfist's him. Feeling confident, Rui challenges Tanjiro to cut of his head, attempts to but fails, due to Rui's neck being far stronger than even his threads, before brutally kicking him away. Nezuko begins to struggle in her restraints, which Rui responds to by tightening his threads, reminding her that he is now her elder brother and commands she cease. When Nezuko passes out, Rui notes she is unlike any demon he has ever encountered.
Calling the Demon Slayers a torrent of insignificant low-lifes, Rui attacks Giyu with Cutting Thread Rotation. Giyu responds with Total Concentration: Water Breathing, Eleventh Form: Dead Calm. Rui angrily shouts that it doesn't matter what the technique is when his own web of threads is destroyed. Shocked and confused Rui moves to perform the attack again, but Giyu disappears in the moment he had blinked. A moment later, Rui is decapitated.
As Rui dies and crawls to Tanjiro, he tries to recall why he did everything in the first place, recognizing the reason as wanting to feel a bond, something he envies Tanjiro and Nezuko for. He reminisces on his past; how he was once a frail boy that was turned by Muzan into a demon, and his parents' reaction to him killing someone, and how he subsequently killed them. He remembers that since doing so, he had longed to feel something he previously has, leading him to form the Spider Family to feel a familial bond but failing. 
Abilities
In the second databook, it was revealed that 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 skillful as Lower Rank One or Two but wasn't obsessed with numbers and didn't 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 Hashira by himself despite him being a Lower Rank. It was also stated that if Rui recovered all of the power he shared with his "family", he could have been a good match for the Hashira, and possibly could have been stronger than them. 
Fighting Style
Rui displayed terrifying proficiency in utilizing his threads for combat purposes, making use of the environment to spawn a barrage of string attacks or manifest unavoidable web techniques to trap and slice his opponents into pieces.