As an introduction to the twelve moons of Demon Slayer, Rui worked perfectly. He had a power unlike what was seen before and even had a network of underlings or family. He gives you a taste of the craziness that is to come later once the upper moons start to get delved into more, and gave a chance to show how heartless Muzan is.

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Perhaps the most striking thing about him though is how sympathetic his backstory was. It isn't something that was all that expected as demons up to that point haven't been more than just villains. For having a smaller role, Rui has lots of depth and plenty of interesting facts about him.

10 Meeting Those He Knew While Disappearing

rui from demon slayer

He's one of only two moons who got to see those he knew in life whilst disappearing, Akaza being the only other one. It shows that while broken and very much a demon, Rui had a very sympathetic backstory. His desire for a family is one that resonates with a lot of people, even if he went about it in completely the wrong way. What happened with his actual family while he was becoming a demon was equally as depressing and sad.

9 Demon Art Inspired By Lubbock

Rui's threads in Demon Slayer

The similarities between Rui's Blood Art and Lubbock's Cross Tail from Akame Ga Kill are vast. Lubbock's wires were used just as the webbing of Rui's was, using it to detect enemies and even used as a way to trap them if someone wandered too close to his web. They could both be hardened enough to slash through people as well. While the ability plays into Rui's spider-like motif, it's hard to ignore how similar the fighting style is between the two characters. Even their special attacks are almost the same.

8 Cell Manipulation

As with Muzan, Rui can offer his blood to strengthen his fellow demons, granting them additional abilities in the process. He also can alter their bodies, changing them to look as he wishes them to.

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This is elaborated on through Daughter Spider Demon as she was made to look as he does, both in size and appearance. It shows how powerful Rui was, even if he was just a Lower Moon rather than an upper. He had far more to offer than his companions.

7 Rank Engraved Into His Eye

Rui's lower five rank is engraved into his left eye, a painful procedure that all of the moons had to undertake when Muzan created them. The interesting part is that the lower moons only have it in one eye while the upper moons have it in both. You don't get a good look at that fact since most of the lower moons are annihilated before they can do anything. It's a subtle way of showing that they are lessers, lacking in strength compared to the uppers.

6 Only Lower Moon To Keep His Human Name

Rui the Demon using webs in Demon Slayer.

Given the circumstances surrounding why Muzan turned Rui, it isn't that surprising that he kept his human name, even as a demon. Changing it would ruin the gift that Muzan supposedly gave the young boy. Despite everything that happens to him and all the changes he underwent both mentally and physically, Rui was always that same little boy under it all. The one thing he'd always strived for had never changed.

5 First True Demon Moon

kyogai demon slayer

Technically he's the second one they met as Kyogai was the former lower sixth and far more impactful than the fodder that Muzan ended up slaughtering mercilessly, but he'd been excommunicated by the time he was fought.

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Rui was the true first look at the power of the moons, an appetizer for the main course later. It's something the series as a whole did a good job off, always slowly ramping things up and not having power levels creep up too much.

4 Voice Actor Showdown

The voice actors for Rui (Koki Uchiyama) and Tanjiro (Natsuki Hanae) have been on opposing sides in an anime before, voicing Shirou Kotomine and Sieg in Fate/Apocrypha. It's not an unheard-of thing in the field as voice actors often do work on plenty of shows, but it's interesting that in both cases, they were on opposite sides of a battle. Both times, the actors brought their A-game as well, helping ramp up the tension of the battle with their work.

3 Symbolism Of His Hair

Rui _ Demon Slayer

Even as a human, Rui had the same spider-like hair, black locks curling inward like the legs of a spider. It's a look that worked perfectly for his demon form, considering what his powers were, but it had a greater meaning beyond that. The hairs showed that as a demon, he'd catch fellow demons in his web, forcing them into his family. That same webbing works as the lies he told himself, making himself believe that his family never cared about him, that they didn't matter.

2 His Fragility

Rui had all of the power in the world, more than most demons could hope for, yet, deep down, he was just as fragile as he was a child. He never managed to outgrow that state of helplessness, never able to become self-sufficient, no matter what he did. Following his rules as law wasn't the only thing his spider family was meant to do, they were supposed to protect him, just like his real family failed to do in his eyes. It furthers how tragic his backstory and character is.

1 He Was The Only Lower Moon Killed By A Hashira

Talk about trying to hit above your weight class, Rui trying to fight Giyu was a massive mismatch from the start and a good way to show how strong the Hashira are. While we only saw two lower moons in action (three if you count Kyogai), Rui's the only one that was taken down by someone who wasn't part of the main cast. It makes you wonder why he was rated as lowly as he was, as you could argue, he was stronger than Enmu.

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