Both Hero Killer Stain from My Hero Academia and Hero Hunter Garou from One Punch Man are doing the same work, though Stain is a bit different.
Is there any difference between them?
Even though both the character are Hero antagonist, still there is quite a difference between these two.
Hero Killer: Stain aka Chizome Akagur
Stain is a cold, unforgiving man with a sense of duty to cleanse society of false heroes. He believes that those who work as Heroes to collect income are unworthy of being called the name and only All Might is a true hero. Due to his strong ideology, he took it upon himself to become Hero Killer: Stain to stain his own hands with blood to purge fake heroes and change the current society.
His reason for killing is his extremist views about the ideal Heroes of Society.
Hero Hunter Garou
Garou is introduced as an evil character with a hatred for heroes and has a confident, vindictive characterization. Garou hates the popular, as he believes the popular will always win in the end. This is because as a child, he had no friends and the popular children at school enjoyed abusing him both physically and verbally, particularly a boy named Tacchan. They forced him to play Heroes, where Tacchan ("Justice Man") would beat up Garou ("the monster"). Garou noticed how everyone liked Tacchan but hated him. After watching his life repeat over and over again on the Justice Man TV show, he grew a distaste of heroes in general and believed that in the end, the majority will always want him ("the monster") dead.
Garou's reason for Hero Hunting are his terrible childhood experiences, that made him a villain today.
In spite of his extremist views and beliefs, Stain does have genuine ideals about Heroism which he stands by firmly. He does not hesitate to save people he deems worthy of being called Heroes, does not like killing without reason, and will even give advice to his enemies. He seems to acknowledge that what he is doing is morally wrong, but believes that in order for society to be put on the right path, someone must be what he is, indicating he sees himself as somewhat of a martyr.
Garou is a villain and considered evil by most, he possesses a sense of morality: he fights heroes in a way without killing them, but he is okay with others killing heroes.
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