Although it would seem that Muzan is the most disliked character in Demon Slayer, fans really claim that Kaigaku is far more hated than the demon king.
Typically, Demon Slayer presents its characters as sympathetic and flawed rather than overtly wicked. Some villains even have likable backstories. Of course, there are some that don’t apply, such as Muzan, the primary antagonist.
But in a way, Kaigaku’s character is worse. That’s because, up until he betrayed both of them, he was close to two important characters, therefore he’s not really a villain. In addition, he is a bottom feeder who advanced in the hierarchy following the defeat of three demons from the Upper Moon.
Kaigaku was raised as an orphan by Gyomei when he was younger. However, he betrayed his caregiver and the other orphans when surrounded by a demon, which resulted in their deaths and Gyomei being wrongfully imprisoned for their killings.
Later on, he turned into a demon slayer and, together with Zenitsu, was adopted by the former Thunder Hashira Jigoro. However, his desire for power turned him into a demon. Old man Jigoro was so hurt and humiliated by Kaigaku’s deception that he committed seppuku.
Zenitsu is permanently changed by Jigoro’s passing. After Gyutaro and Daki die, he eventually confronts Kaigaku in the Infinity Castle Arc. Kagaku has evolved into the Upper Moon Six demon. Observing their battle is a sight.
The terrible pasts of not one, but two of the main characters in the novel were connected to Dude. I’m ready to watch this guy go down, no spoilers,” a Reddit user said in reference to Kaigaku.
“F**k this guy, first he betrayed Gyomei and then how this mf treated Zenitsu,” said a second.
Another person said, “The beating Gyomei gave the demon in the temple should have been meant for him, lol.”
“Sh*tty as a human, sh*tty as a demon,” penned a fourth.