My Hero Academia's manga has been in a villainous arc as Shigaraki and his League of Villains are doing battle with a new faction vying for the top spot, the Meta Liberation Army. While Shigaraki has been tested to lengths that he has never been tested before, each chapter of the series has surprisingly begun to explore different aspects of his origin. Along with revealing his early life with his family before his time with All For One, the series has revealed the origin of his quirk.
There were interesting ties between Shigaraki and Izuku Midoriya made more concrete as it seemed like Shigaraki's Quirk didn't develop until a late age, but in Chapter 235 it's revealed that his Quirk manifested as a response to extreme emotional and physical trauma.
Chapter 235 of the series dove into Shigaraki's darker home life as he lived with his loving family, darker elements were bubbling under the surface. Because he wanted to be a hero, his father constantly abused and punished him because his father was still reeling from the abandonment and loss of his mother, Nana Shimura. He wanted to teach Shigaraki to avoid this life, and chose to physically harm him in order to get the message across.
After a particularly rough punishment in Chapter 235, the young Shigaraki (five years old then) began to feel itchy even more. It's implied that this itchiness is tied into his quirk, as it's getting worse, and soon his hand begins to tingle as he plays with his dog, Mon. Following this reveal, Shigaraki's father abuses him once again and his hand begins to twitch and writhe in this itchiness as his Quirk begins to activate.
Chapter 235 revealed that Shigaraki's Quirk still had not developed even though he was five years old, and it seemed like he was on the same path as Midoriya. But with this extreme traumatic stress, his Quirk sparked within him for better or worse.
My Hero Academia was created by Kohei Horikoshi and has been running in Shueisha's Weekly Shonen Jump since July 2014. The story follows Izuku Midoriya, who lives in a world where everyone has powers, even though he was born without them. Dreaming to become a superhero anyway, he's eventually scouted by the world's best hero All Might and enrolls in a school for professional heroes. The series has been licensed by Viz Media for an English language release since 2015. My Hero Academia is gearing up for an even bigger end of 2019 with a new film in theaters later this year too.