One of the most captivating aspects of Demon Slayer is its ability to make antagonists extremely likable to the audience. The anime effortlessly gives those defeated by the Demon Slayer Corps endearing backstories, reminding the viewer of their humanity. More often than not, they never wanted to live as demons but were transformed against their knowledge or at the hands of Muzan Kibutsuji.
Demon Slayer fans globally became drawn to one particular clan of demons, with the head being of particular interest. The spider demons were the main antagonists in the "Natagumo Mountain" arc, giving Tanjiro, Zenitsu and Inosuke a fair share of challenges to overcome. However, Tanjiro Kamado's battle with Rui, the creator of the clan of spider demons residing in the mountains, was truly remarkable.
Rui Shares a Spider's Poor Eyesight and Reliance on Sound
Despite his childish appearance, Rui was a member of the Twelve Demon Moons crafted by Muzan Kibutsuji. As Lower Moon Five, Rui was the strongest demon Tanjiro had faced yet in Demon Slayer, but incredible strength was not the only thing Rui inherited from his demon form; his life as a spider demon may have left him with some peculiar attributes unseen in other demons.
Specifically taking the form of a spider demon gave Rui some heightened senses, but also left him at a disadvantage in some cases. Rui had poor vision -- and his tactics reflected this. He used attacks with broad range that would often go in a sweeping motion, opening up the area of effect. Even his blood demon art, Murderous Eye Basket, was a ranged attack, steadily getting smaller until the target was inevitably trapped in threads and cut into pieces.
This blood demon art reflects more than the type of demon Rui is -- it's obvious a spider would use webs in their attack -- but further reflection pins Rui's method of attack on his poor eyesight. Spiders are extremely nearsighted, to the point where they rely on other senses like touch and sound to survive. This is where Rui's similarity to spiders truly takes form.
Rui also has highly sensitive hearing and uses vibrations to locate and analyze his opponents. While all demons have a heightened sense of hearing, no one else appears to be as irritated or skittish around loud noises as Rui. While he relies on his hearing to sense when an opponent is approaching, it's likely also extra sensitive to make up for his poor eyesight.
Rui's Spider-Like Attacks in Demon Slayer
Rui relies on both his hearing and vibrations while in combat. He rarely attacked Tanjiro directly, instead taunting him into moving so Rui could pinpoint his location through vibration. When he did attack Tanjiro physically, the protagonist was consistently within a certain range -- close enough for Rui to see him.
The spider demon also knew when Nezuko was conscious without looking at her as he could sense her movements, or lack of, through the vibrations in his threads. This gave him an upper hand in combat, shown when he sensed another slayer sneaking up on him and wiping him out without a second glance. Rui thrived as an opponent due to the habits being a spider gave him, and his heightened senses made Rui a formidable opponent that only a Hashira could defeat.
Rui is another example of exceptional writing and character development within Demon Slayer. A tragic backstory combined with spider-like attributes made him an excellent antagonist and gave Tanjiro the push required to unlock his most important ability, the Hinokami Kagura. Future anime arcs are likely to bring a similar depth to demons, transcending the trio's abilities with every fight.