Hero Killer Stain is a villain from Boku no Hero Academia. He is a criminal who has killed many professional heroes that he deems fake.
Chizome truly respects All Might from the bottom of his heart. He sees him as a true hero who does heroics for the sake of saving lives not for money or status like the other heroes. At some point, Chizome was disgusted by the individuals who calls themselves heroes and thought about his ideology of creating a new world filled with true heroes by killing off all other heroes who he deems fake.
While he is vice and ruthless in murdering and beating his victims, Chizome have shown to respect others who are willing to fight to save someone's life like Izuku and was willing to spare his life in their battle. However, he can be utterly disgusted by heroes who are out to stop him for their own selfish purposes and has no compunction towards killing them.
While Chizome despise heroes who are out for fame and money, he also dislikes villains who are out for unnecessary violence and bloodshed like Tomura Shigaraki.
Chizome was first mentioned in an incident where he nearly killed Ingenium. He later appeared on a building in middle of town. He began stating how people are misguided and that he will be the one to show them reality. He was approached by Black Mist who asked that they could meet elsewhere. They made it to a hideout where he met Tomura who was interested in making him join his group the League of Villains. Chizome did not like Tomura's goals of destroying All Might and other people who stands in his way. Their meeting ended up becoming physical when Chizome had pinned down Tomura. As the meeting with the League of Villains ended, he asked to be returned to Hosu so that he could resume his work.
Chizome cornered a hero in the alley that he deemed a fake. He was about to kill him until Tenya decides to confront him. Chizome did not want to fight the teen but the latter was insistent on getting vengeance on for his older brother, Igenium, that he nearly killed. After getting into a skirmish, Chizome decides that he would kill Tenya since he did not uphold the true values of a hero and was blinded by vengeance and vigilantism. Izuku appeared soon enough to prevent Chizome from killing Tenya. The fight continued when Chizome overwhelmed Izuku. He decides that he would spare Izuku's life since he is a true hero who is willing to save his friend. Chizome turned his attention back to attempting to kill Tenya and other individual. Shouto also appeared as a back up to stop Chizome from killing the men. The fight dragged on for nearly ten minutes until Chizome was knocked out by a combined attack from Izuku and Tenya.
After the fight, Chizome was immobilized and taken by the men and was about to be handed over to the police. When one of the Noumus tried to kidnap Izuku, he got up and immediately attack the Noumu. He saved Izuku and then decided to take him as a hostage. Chizome then let out an intense amount of blood lust which left everyone there in fear. Before collapsing from his injuries, he said that he would not want to be killed off by any of the fake heroes and that he deserves to be killed off by All Might. After collapsing, Chizome was taken into custody by the police. His detainment became one of the major news outbreak throughout Japan and other places.
After his arrest, Chizome's ideology would become an inspiration to many villains and an excuse to commit horrible crimes against the public.