Tanjiro Kamado from the Demon Slayer anime is getting a lot of praise this season for being kinder and more sympathetic to his enemies. And compared to most shōnen protagonists he is. But he is hardly an outlier in demographic that covers everything for the run of the mill battle series to touching character dramas. Even though he isn't an outlier, I could get behind Tanjiro’s philosophy of sympathy towards his opponents. But, his opponents are unrepented murderers and manipulators.
The show tries to get us to empathise with the antagonists by giving us a sympathetic moment during most demon’s deaths. Either in the form of a flashback – showing us why the demonic path tempted them. Or a tender moment – the returning of a beloved object, or a spirit calling to the demon from the other side. However, because these demons are so unlikeable this moment comes off more as a moment of pity, rather than being empathetic towards their suffering. And to me, pity is a negative emotion compared to empathy.
Instead of delving into why these demons might be deserving of our empathy, we are barraged with a series of unrepented and ruthless killers. Their demonic transformation twisting their human desires. They existed for decades or centuries, killing humans for food with little care beyond fulfilling their warped desires.
To remind you our rogues’ gallery of deplorables includes...

What little insight we get into what tempted them onto the demonic path comes too late in the narrative to effectively sympathise with their motives. Or the answer is petulant, thus making me unable to empathise with their plight.
Kyogai, the Drum Demon, has a flashback that is especially typical of this petulant motive. Though by the time of the flashback he was already turned we do get an insight what might have been his motive in taking Muzan’s dark promise of power and eternal life.
As a human, Kyogai was a writer and drum player. Still, he never received any recognition for his artistic works. He is chastised – by what I assume is either his editor or father – for his average quality in the arts and kills him because of it. He then; until Tanjiro slays him; keeps on killing, only achieving his dreams when Tanjiro recognises his demon arts as amazing. This statement redeeming him in a way, allowing him to cross into the next life unburdened.
But because his initial reasoning is petulant, I can’t even feel pity for this character. Nor do I feel happy he is able to move to the next life unburdened by his crimes. His petulant reasoning of being slighted by society making me unable to feel sympathy or even pity for his death.
Rui, the Spider Demon, is one character that does have a genuinely sympathetic backstory. Having been a sickly child accepting Muzan’s offer gave him the freedom he never had before. But because of his need to consume humans to survive, his parents became appalled by his new form and tried to kill him. This and Muzan's prodding lead him to think their bond wasn't genuine. He fulfils the gap left by inducting demons into his performative family.
And this would have been a genuinely sympathetic backstory had Rui’s actions before this flashback been more compassionate and caring towards his found family. Instead of up until his death, what we are shown is a cruel, calculating, manipulative, and abusive demon. Who kills unrepentantly and punishes those around him for not obeying his every command. Consequently, his motivations aren't backed up by his actions.
Even if you accept that his mistrust and need to control is a result of his parents attempt to kill him. The revelation of Rui’s motives comes too late in the story to truly sympathise with him. So, when his sympathetic flashback comes, it’s hard to feel much for such a cruel being just because he started with good intentions.
Instead, it is much easier to sympathise with the Mother Spider Demon and the Older Sister before their sympathetic deaths as we get glimpses into the why of their actions. The Mother Demon is tormented and abused by her adopted family for every misstep. She is pushed into acting perfectly on Rui's behalf. So when her death comes not only is it a relief to the audience but to herself as well and feels rightfully merciful.
Even the Older Sister, who is manipulative and desperate to stay within Rui’s inner circle, has understandable motives even if I don’t sympathise with her. By the point, her sympathetic flashback is shown the audience has already seen Rui abuse her and the Mother Demon. Thus, when we see her betray her only friend amongst the Spider Family in the flashback. Her motivations to stay within Rui's inner circle are clear. Outside and alone, she risks being killed by Demon Slayers, but if she gives up her autonomy and obeys Rui, she is safe.
The Older Sister Demon may have been unredeemable and deserving of death. However, her actions are born from desperation rather than petulance. Her malicious self-preservation, above all else, is what leads her down the path of ruin. And though she suffers under Rui's domineering and demanding rule to her, the alternative is even worse. And because of this, she is an unredeemable but sympathetic villain.
It’s perfectly fine to have antagonists that are redeemed or even grow to be sympathetic characters, even if their actions are ultimately wrong. However, this doesn’t work unless you build up a reason why we should care. If we only see one side of a character before their sympathetic moment, that moment doesn’t work. And there are plenty of ways, and demons Demon Slayer could use to spread genuinely sympathetic demons amongst its cast of unrepented murders. It is apart of the premise, after all.
However, Nezuko, the main reason why we should sympathise with demons is mostly regulated to her box or used as plot armour for her brother Tanjiro. Throughout 26 episodes, we never spend enough time with her to understand the real horror of her forced transformation. Consequently, she is an inefficient demonstration of why demons can be sympathetic.
And this under development or petulant motives for antagonists Demon Slayer wants us to sympathise with is why I ultimately I couldn’t sympathise with Demon Slayer’s antagonists.