"My Hero Academia" recently revealed that Shigaraki Tomura's quirk, Decay, was created by All For One using a quirk factor taken from Kai Chisaki, also known as Overhaul. Both Decay and Overhaul's quirk allow them to destroy with a touch, showing their power and similarity. Chisaki, raised in one of Dr. Garaki's facilities, was experimented on and forced to escape, developing his obsession with quirks. This upbringing led to his unethical actions, including experimenting on Eri and putting his father figure in a coma. Despite losing his quirk to Shigaraki, Chisaki showed no remorse, highlighting his irredeemable nature. The dark origin of Overhaul adds depth to his character in "My Hero Academia," creating an intriguing and complex villain in the series. The show follows Deku, a hero-in-training at UA, as he learns what it takes to be a hero and confronts dangerous supervillains.