Many shonen anime series, including the ever-popular Demon Slayer franchise, create meaningful parallels between the hero and their villains. This helps remind shonen fans that for all their differences, the heroes and villains are all people - even if they're not technically human. Deep down, these feuding parties can understand one another, and that can make the fight personal and thematically resonant.
Source：https://www.cbr.com/demon-slayer-tanjiro-kamado-villain-parallels-ranked/
