Demon Slayer tells the story of the charcoal vendor turned hero Kamado Tanjiro, and he has fought many heroic battles for the sake of humanity, but what drives him most of all is the quest to restore his little sister Nezuko's humanity. Tanjiro is a wonderfully protective brother, but he's not the only one.
Tanjiro is also a compassionate slayer who listens to each demon's personal story before they die, and many of these demons are secretly vulnerable and hurting on the inside. All of them had someone precious to them, and now, the mighty Upper Moon Six demon Gyutaro has someone to protect -- his sister Daki. He is what Tanjiro might have become under different circumstances, and deep down, Tanjiro may sympathize with him.
Gyutaro, The Dark Reflection Of Kamado Tanjiro
Tanjiro and Nezuko make a great team, and few, if any other Demon Slayer characters have the same dynamic. Most demons are solitary hunters and won't fight for the sake of others, and most demon slayers fight only for duty's sake and don't have someone personal to protect. Tanjiro is a relatable shonen hero by fighting for his beloved sister's sake, but now, he has met his match. In a series first, a demon has a precious sibling to fight for, and his name is Gyutaro.
Gyutaro and Daki are a brother/sister team sharing the rank of Upper Moon Six, and Daki's powered-up form is just the start of Tanjiro and Tengen's battle in the entertainment district. But these two demons are more than a boss fight -- they also represent what the Kamado family could have been. Already, Nezuko is a full-blooded demon with a ferocious side, and if things had gone differently, perhaps Tanjiro could have gone the same way.
When Muzan attacked the family, no way could Tanjiro have fought him off, and if Muzan didn't simply kill Tanjiro, he would have made Tanjiro a demon as well, and the two surviving Kamados would be a demonic brother/sister team just like Gyutaro and Daki are now. They would even have the same interpersonal dynamic, as Tanjiro was highly protective of Nezuko even before she became a demon.
It's conceivable that a demon Tanjiro might have willingly become Muzan's subordinate so he could gain the necessary strength to defend Nezuko, and he might have been on the path to becoming a Moon himself along with Nezuko. Even if Tanjiro rejected Muzan and went rogue with Nezuko, they'd still have a Daki/Gyutaro dynamic and be the target of demon slayers everywhere without the benefit of Muzan's protection. In either case, Gyutaro and Daki prove that brother/sister demon teams are a reality, and Tanjiro beheld what he and Nezuko could have ended up being. The sight of it should chill him to the bone.
Tanjiro Might Still End Up Like Gyutaro
Tanjiro has done much to establish himself as a compassionate shonen lead who doesn't harm others without good reason, and he sees the good side in absolutely everyone, even the demon that killed Urokodaki's previous students. However, most shonen heroes have a hidden dark side that they will tap into during an emergency, and Tanjiro may not be exempt. This has not happened yet, but given Tanjiro's intense personal stakes where Nezuko is concerned, he just might fly into a berserker rage and fight like a demon for her sake. Everyone has their limit, and at this rate, Tanjiro might soon hit his own. His compassion can only last for so long before he snaps and becomes a brutal, over-protective brother like Gyutaro, even if he remains fully human.
Already, Tanjiro hinted at this dark side after Kyojuro's battle with Akaza, when Tanjiro recklessly threw his Nichirin sword and impaled Akaza's retreating back in rage and desperation. Tanjiro also shouted himself hoarse at the fleeing demon, calling him a coward, and that wasn't even for Nezuko's sake. Kyojuro was important to Tanjiro, but Nezuko is even more so, and there's no telling how demonic Tanjiro might act on her behalf if she's threatened.
So far, Nezuko has not been threatened directly, such as being held hostage or tortured, but if that happens, Tanjiro might go full Gyutaro and become a demon at heart for his sister's sake. If so, he may put even Gyutaro's brutality to shame and show Gyutaro what a vicious brother really looks like.
