There are many deep themes of human lives that have been portrayed in the anime Kimetsu no Yaiba, with the heart-wrenching backstories of the demons, their origins, their justifications of why they became demons, it’s a blend of good and evil and human perceptions that proves that neither is the right morality. Among the demons, each and every story of how and why they became demons were portrayed beautifully which the viewers saw from the eyes of the main protagonist, Tanjiro.
One such demon that Tanjiro encountered is the Lower five: Rui, who was one of the Twelve kizukis under Kibutsuji Muzan with a high concentration of his blood that makes them extremely formidable and hard to defeat. Despite his hostility, cold outlook, abusive and forced familial bond for using them against the Demon Slayers, ruling them with fear and instilling a corrupted sense of love which was nothing but abuse and possession, Rui is a demon whose such instincts rooted in his tragic past of abandonment and deceit.
Rui and his incarnation of the definition of family
Among the demon family, he was the eldest brother who collected demons and bound them into a promised bond and if any of them betrayed him, they would be slit and exposed to the sun and would face a slow and painful death. His obsession with ruling the ones with a false and imposed sense of love makes the viewers wonder about his previous life and what made him choose the painful immortality rather than the beautiful mortal human life with guaranteed hate?
The demons who chose this path have been filled with hatred towards the human race because of its treachery and corruption, which hits the sense of morality again, that it’s not wrong. Humans are corrupt and magnificent creatures of deceit. But as his backstory reveals his weakness, viewers immediately create a sense of empathy for him. Family means unwavering loyalty, sacrifice, and care, which Rui strongly believed. But his strong and daunting belief turned into an obsession that ultimately caused him to lose his family.
Rui was a disabled child who could not stand the exposure to daylight. His disability led him to stay trapped and depend on his family for his care. He used to watch the children play and wanted to play with them, he wanted to be able to do everything that a normal human was capable of doing. Day by day, with grief and loneliness, he became hostile when Muzan approached him and granted him the power of a demon, where he could move as freely as he could, he just had to devour humans.
When things unraveled and his parents could not stand their son being a threat to other humans, his father decided to kill him in his sleep and themselves afterward, but Rui’s senses grew stronger and he killed them. After a while of crying, his demonic soul took over, killing anything humane left in him. With this, he went on in search of a pretend family where he would bind them in a filial bond and if they betrayed, he would give them the punishment they deserved, as families are supposed to be loving and sacrificial when they need to be.
Reawakening and reunion
Rui’s brotherly senses got reawakened when he saw the deep bond that Tanjiro and Nezuko shared, driving him to take Nezuko as his sister and bind her to his blood. During the first years of him fabricating the family under pretense and forged bonds, his trust was gained by his demon sister who was trapped under the same bond. She betrayed a fellow female demon with whom she planned to escape, but rather made herself more trustworthy to Rui. Through this trust that he placed, he expected never to be disappointed.
His abusive and toxic obsession to control a relationship comes from the lack of warmth and love that he had denied. When he saw the bond that Tanjiro and Nezuko shared, he got more paranoid to get Nezuko to be his sister, even when his sister of the forged bond was standing, ashamed for not being able to be useful to him. He asks her to kill as many slayers as she can to win back his trust. He made his relationship with people sound like the other always had to get his validation, which he wanted the same with Nezuko.
When he put up his fights but in vain, seeing the depth of the bond that the siblings shared, he got enraged and decided to kill them both with his blood demon art. His vile attacks kept on going when Tomioka made his timely appearance and beheaded Rui with his Water Breathing Eleventh form. In his final moments, he traces his time back and gets reacquainted with his conscience, and seeks forgiveness from his parents. Ultimately through a teary lens, it is shown his parents never forgot him and forgave him long back, and they got reunited.
With the demise of every demon, they get reunited with their human side and bid farewell to their sins, which is a beautiful closure that the creators of Demon Slayer provided to their conflicted characters.