Tanjiro's relationship with demons has been unlike any other member of the Demon Slayer Corps during Demon Slayer. After all, he became a Slayer because his sister has turned into a monster, and he hopes to discover a means to restore her humanity. Tanjiro is in a unique position to comprehend and empathise with demons since he is so close to them. He won't give up on his sister, so why should he give up on other demons?
Tanjiro is able to demonstrate compassion towards demons by recognising their humanity—even when he must slay them. This idea of empathy for one's adversary pervades Demon Slayer, and it has resulted in Tanjiro experiencing personal moments with the demons he slays as they suck their dying breaths. However, Tanjiro's lack of compassion in slaughtering Hantengu, the Upper Rank 4, in the season finale of the Swordsmith Village Arc, seems to completely break this pattern. Whether that break from precedent was prompted by Tanjiro's feelings at the time or by Hantengu's own background as a human, it's certain that Tanjiro's attitude towards this demon was unlike any other thus far.
Tanjiro's Sympathetic Approach To Slaying Demons
From the very first demon he killed before even passing Final Selection, Tanjiro showed the kind of compassion that most people in his world would never show to demons. His encounters with each subsequent demon afterward would see Tanjiro provide the demon with a last means of comfort and peace in their final moments. Two prominent examples of this are his interactions with the drum demon, Kyogai, and the Upper Rank 6 demons, Gyutaro and Daki.
In Kyogai's case, Tanjiro gave the demon in solace in acknowledging the power of his drumming, even though he strictly condemned his murderous ways. Similarly, Tanjiro helped bring Gyutaro and Daki together before they passed on, helping them see the value in their relationship as brother and sister. In both of these cases, Tanjiro makes a clear effort to go out of his way to show kindness to his enemies, helping them find peace despite the terrible sins they've committed.
Why Tanjiro Had No Sympathy for the Upper Moon 4
Despite Tanjiro's ordinarily compassionate attitude toward demons, he did not offer the same solace to the Upper Rank 4, Hantengu. Instead of leaving it with kind words or sentiments as he has done with the others, Tanjiro simply beheaded his foe, offering it only the words "Atone for your sins, with your life!" This is a far cry from his previous interactions with the demons he has killed—but there are at least two compelling reasons that explain why he made that change.
The first has to do with his relationship with Nezuko and his mental state upon his belief that she was killed. Tanjiro's lack of compassion at that moment could have been a hint at how hardened he would become without his sister to keep him grounded. This shouldn't come as a surprise; Nezuko was always Tanjiro's reason for taking on his role as a Slayer from the very beginning, so losing her would not only negate his connection with the other demons but also remove his initial purpose for fighting so hard. A second, equaling compelling reason for Tanjiro's apparent lack of compassion is in relation to Hantengu's life as a human being. During his lifetime, Hantengu was a murderer who would never admit to his crimes, instead pleading for sympathy and claiming that it wasn't his fault. Being that Hantengu was obsessed with insisting on sympathy that he didn't deserve, perhaps Tanjiro's method for saving him was to refuse to give him what he wanted. In this way, it was more a form of tough love than an entire lack of empathy.
In all likelihood, it's a combination of both of these factors that caused the actual change in Tanjiro's disposition toward this particular demon in contrast to the others. His pain at the loss of his sister coupled with Hantengu's disingenuous personality is what pushed Tanjiro into the kind of mentality that left little room for sympathy for the Upper Moon 4 demon. Though Tanjiro was able to focus on completing the job that his sister entrusted him with in her perceived final moment, he immediately broke down afterward, showing that Nezuko was—and always has been—his ultimate reason for remaining strong.
