They Wasted A Perfectly Good Character / Demon Slayer: Kimetsu no Yaiba

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• Except for Enmu and Rui, the remaining Lower Ranks are slaughtered by Muzan in their first appearance, without giving them the chance to show their abilities or background.
• Likewise, some of the characters who were killed off in their only episode appearance can be treated this way, as there could have been potential within them. One example is Ozaki, the girl who is forced against her will into attacking her comrades. Another example is any of Tanjiro and Nezuko's deceased siblings.
• Kaigaku, the replacement Upper Rank Six, is seen as this by many. Though Zenitsu makes note of the history between them, the first time he is properly introduced to the audience is in the very last arc of the series, with only a few small cameo appearances prior. From there, he puts up a fight for no more than 3 chapters before he's dispatched in one blow.
• Upper Rank Five Gyokko feels like this for some fans. Unlike other Upper Ranks who offered incredible battles and proved to be fearsome enemies, his fight against Muichiro was very one-sided from beginning (where Gyokko easily overpowered the Hashira) to end (where Muichiro in return defeats Gyokko swiftly once he awakes his Mark), making him a plot device to introduce the Demon Slayer Mark and to show how strong Muichiro is after awakening it. To make things worse, nothing about his backstory or past was revealed through his screentime, leaving him as a less compelling character even compared with less relevant antagonists like Kyogai or the Spider Mother.
• Urami, the embodiment of Hantengu's resentment receives the least characterization and screen time out of his emotion clones, being little more than a last ditch summon by the cowardly demon to defend himself. He had the potential to be an interesting and formidable foe as he is shown to be Hantengu's very last body guard, and one who seemingly has all of (albeit weaker) the emotion clone's powers. In addition he's the only emotion that doesn't need to be assimilated to form Zohakuten, so we could've seen how the two work off each other in combat as it's revealed that Zohakuten's power drains Urami of his strength and possibly vice versa. Due to his limited presence, Urami is often excluded from fan works that involve Hantengu's emotions.
• Nakime the Biwa demon. She appears way before the Upper Ranks, seems to be Muzan's most trusted subordinate, and after Hantengu's death she's ascended to the rank of Upper Rank Four. However, once she gets her turn to fight, she barely does anything other than toy with Obanai and Kanroji, with their "battle" essentially being considered comic relief and then she's killed by Muzan without second thoughts once Yushiro takes control over her body, without the audience managing to learn anything about her personality or backstory.
• Some have said that Doma, being a cult leader and having a very entertaining personality, would have served extremely well in a standalone arc that involves the demon slayers investigating a mysterious cult. As is, he just gets a brief fight against Kanao and Inosuke, being bunched into the final arc like the rest of the remaining Upper Ranks.
• There are fans who view Tengen Uzui's remaining brother as this, being given a unique design and interesting backstory during his very brief appearance in Tengen's flashback. He is also described as having no humanity remaining, giving some the impression that he would return later on as a demon, a ninja demon. The fact that the new Upper Rank-5 who replaced Gyokko was never revealed only fuels this, as some speculated it would be revealed as Tengen's brother at some point. There was even a potential set-up in the final arc for the two to meet again if that were the case; Tengen protected the vulnerable Kiriya during the events of the final battle and many had hoped the new Upper Rank would finally show up to make an attempt on his life, and Tengen's brother being that demon would've brought his story full-circle, facing and ending the monster that he could've become under his father's influence. But neither plot point involving the brother or the new Upper Rank were ever addressed after their initial mention, leaving fans disappointed. The second fan book finally sheds some light on what happened to Tengen's brother, revealing that there was an incident where Uzui seriously contemplated killing him and their father, but ultimately did not have the heart to go through with it.

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