Rui

Rui is the primary antagonist in the Natagumo Mountain Arc of Demon Slayer: Kimetsu no Yaiba. He is a demon affiliated with the Twelve Kizuki, holding the position of Lower Rank Five (の).

Appearance
Rui has the appearance of a young boy of short stature. His skin is white, with red dots. His hair is light pink and bears resemblance to spider legs. The sclera of his eyes are red, while his irises are pale blue. Due to holding the position of Lower Rank Five, Rui has the kanji of Lower Rank and Five engraved into his left eye, signifying his ranking of Lower Rank Five.

As a human, he possessed normal black hair styled with the same spider-leg like haircut, with bright blue eyes. He heavily resembled his human father.

Personality
On general basis, Rui is a quasi-calm individual, rarely raising his voice, and talking with everyone, demon or Demon Slayer, with a reasonable tones and vocabulary, though his low and guttural tones constantly imply repressed anger and annoyance. Every time he spoke with Tanjiro during their duel he remained somewhat civil in speech, never once insulting him or calling him a name.

Rui was a disturbed 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 Rui 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 and founded on nothing but fear of him, instilled through repeated abuse on his fellow kin, which he does with unrepentant sadism.

Well aware of his power, he is incredibly authoritarian and cruel and has no qualms about mistreating others or punishing 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 tends to act almighty and confident, although this arrogance, while hardly unfounded, does not blind him to potential threats to his life. Further, he is aware on some level that, despite telling Tanjiro when he saw Rui punishing Spider Sister that he wasn't watching a play, that his whole family is a sham, yelling at Spider Sister that none of his family member were able to fulfill their roles, or fill the void in his heart.

Because of this, Rui is incredibly sensitive to the subject of family and was furious when Tanjiro Kamado 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 contrasts heavily with his desire to have Nezuko Kamado 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 is further evidence to Rui's delusions, mental insanity, and emotional instability.

In death, Rui did feel remorse for his actions, remembering a previous Spider Family member he had strung up to die in the sun because she attempted to leave him due to his ongoing abuse.

Human Life
Many years ago, Rui was born to a somewhat affluent family. He had a weak, frail and easily stressed human body that 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.

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 bringing joy and happiness to his parents. However, this did not last, as he was now a demon, Rui now needed to obtain sustenance by eating humans which then caused him to kill a man inside his home. This bloody scene was then discovered by his parents who were immediately horrified by what their son had done. That night his father and mother agreed that Rui had to be stopped and attempted to kill him in his sleep to prevent him from doing anything worse in the future.

His father then attempted to sneak up on him with a knife and told him not to worry for he planned to also kill himself in turn for killing his son, while his mother was sobbing and crying outside his door. However Rui awoke and in anger for their attempt on his life, killed them both instead in self-defense, rationalizing that his true parents would never try and kill him and thus considered them to be faked in denial.

However, as his mother lay dying Rui overheard her regretfully apologizing to Rui for not being able to give him a healthy body as she died, which then caused him to remember his father last words, promising that both he and his wife would follow Rui to the afterlife by killing themselves, caused him 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. However, Rui persisted on the lie that his bond with his family was fake due to receiving words of encouragement from Muzan, who supported his initial denial that they couldn't possibly be his family due to not accepting his state as a demon, and gave him encouragement to simply look for a new family.

Demon Life
Now as a demon, Rui continued to kill and eat humans to gain more strength until he finally obtained the position of Lower Rank Five and joining the Twelve Kizuki after being acknowledged by Muzan. Due to repressing his painful memories as human, Rui requested to Muzan if he could create a "family" for himself. The latter then allowed him and he began to gather suitable "family members" who would each take the role of his new parents and siblings.

It was shown that he stumbled upon a lone female demon while she was fleeing from a group of Demon Slayers, he then simply asked her if she wanted to be saved by him and if she agrees she'd have to do everything which he says. Desperate for her life, the demon agreed, Rui thus then easily dispatched the group of Demon Slayers easily and warmly welcomed the female into his "family". He then proceeded to give her a small drop of his blood to strengthen her power and painfully alters her physical appearance to resemble his own and officially acknowledged her as his new "Older Sister".

Later Rui was informed by the Daughter Spider Demon about how one of his other older sisters was planning to escape the mountain and leave the family, enraged by this he proceeded to intercept this attempted escape and violently beat the Oldest Sister Spider Demon before stringing her up and leaving her to burn by sunlight of morning.

Abilities
Overall Abilities: Due to being one of the Twelve Kizuki, Rui is one of the strongest demons in existence. This strength easily surpasses that of other demons, since he was easily able to conquer and cohere numerous demons of Natagumo Mountain and force them to work for him and become his family. Evidence of his strength is further shown when he was able to easily overwhelm talented fighters like Tanjiro and kill scores of Demon Slayers with ease. Despite holding the second lowest position in the Twelve Kizuki, Rui possessed the same skill level as Lower Rank One and Lower Rank Two.

Demonic Blood: Similar to Muzan, Rui can augment and strengthen a fellow demon's overall power and give them access to new spider-related abilities by giving him a drop of his own blood, having done so in order to strengthen each and every one of his "family" who were all originally weak demons.
 * Cell Manipulation: As revealed by the Daughter Spider Demon, Rui has the ability to manipulate and change the physical appearance of other demons who consume his blood, having altered the physical traits of his "sister" to match his own. He also likely did the same to his other "family" members to resemble him.
 * Power Distribution: Its been revealed that in terms of ability and power, Rui is in fact as powerful as Lower Rank One or Two despite being ranked as the second weakest member of the Twelve Kizuki and he could actually have put up a decent fight against Hashira level Demon Slayers. However due to him having shared his blood with his other "family" members and giving them access to his spider thread Blood Demon Arts to strengthen them, Rui had in fact given them portions of his own strength. This had greatly weakened him to the point that he could no longer even put up a decent battle against Giyu by the time of his death.  Later despite his "family" members having been killed, the powers he bestowed to them hadn't return to him. This could mean that he permanently loses his powers should the family member he shared it be killed by a Demon Slayer.

Enhanced Durability: Rui possesses a body that is incredibly durable and hard to cut, with it easily far surpassing the hardness of lesser demons, as Tanjiro noted that Rui skin was much thicker that of his "Father", Rui even admitted 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 has displayed superhuman strength, being able to easily overpower Tanjiro by simply kicking and punching him, causing him to bleed with every blow.

Menacing Aura: Rui possesses an aura that Tanjiro was noted to make the air feel thick and heavy with a mere gaze.

Unlimited Stamina & Endurance: All demons have a shared physical trait of endless and limitless stamina and vitality, simply being unable to accumulate fatigue or get tired no matter how hard they try to exert themselves. demons can also endure pain and discomfort better than humans and even the likes of Hashira, taking on onslaught of attacks as if they were nothing.

Blood Demon Art


Thread Manipulation: Rui's Blood Demon Art allows him to create thin threads indiscernable from string from his own cells, and manipulate them however he pleases. He typically extends the threads from his finger tips like a puppet master. Due to his own body's durability, the threads Rui manipulates are 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 pumping his blood through them, giving them a blood red color.

Rui has 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.

Techniques

 * -|Description =
 * 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.

Game Exclusive Techniques

 * Thread Dash (り) - Rui unleashes a three-pronged thread attack from afar.


 * Web Toss (ち) - Rui throws multiple sharp spider webs at his target in succession.


 * Thread Barrier (の) - Similar to his Murderous Eye Basket technique, Rui creates a spherical cage from threads in front of him that expand outward to cut his target to pieces.


 * Cutting Thread Cage, Prison (・) - Similar to his Cutting Thread Cage technique, Rui creates a prison of sharp threads that surround his target and slices them to pieces.
 * -|Demonstrations =

Trivia

 * Rui's name means "accumulate" (累).
 * Rui was ranked in 16th place as of the first character popularity poll with 191 votes.
 * Rui is one of two members of the Twelve Kizuki who met the people he knew in life while disappearing; the other being Akaza.
 * Rui's Blood Demon Art may have been inspired by the Imperial Arms of Lubbock from Akame ga Kill!, Cross Tail, as both grant the user the capability to wield steel threads from their fingertips, and both users use this power in a similar manner to one another.
 * In terms of ability, Rui is as skillful as Lower Rank One or Two, but didn't fight them to switch ranks as he wasn't obsessed with numbers.
 * Rui actually had enough power to put up a good fight or even match the Hashira, however, since he shared his power with his "family", he was left in a weakened state and was unable to even put up a fight against Giyu.
 * Despite being killed, the powers he bestowed to his family members didn't return to him. This could mean that he permanently loses his powers should the family member he shared it to be killed by a Demon Slayer.
 * This also meant that if Rui was defeated first, the other Spider Demons would be unable to use the Blood Demon Arts that Rui gave them.

Quotes

 * To himself) "Long ago, I heard a wonderful story. There was once a father who died trying to save his drowning child. I was deeply moved. Such astounding parental love. And such a bond, as well. This father who drowned in the river had fulfilled his role as a parent. And yet, for some reason, my own parents... My own parents... tried to... kill me."
 * (To himself about Muzan Kibutsuji's encouragement) "I couldn't bear the weight of what I'd done. Even knowing that I only had myself to blame... Every single day. I missed my parents so much that I could barely stand it. Even after creating a fake family, the feeling of emptiness wouldn't go away. 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. Even though it was simply out of my reach no matter how I strained to get my hands on it."
 * (To Tanjiro Kamado) "Family... A father has his role as the father, and the mother has her role as the mother, and the elder brother and sister protect their younger siblings. No matter what. At the risk of their own lives. The way I see it, if you don't understand your own role, there's no reason for you to live."

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