Soga Kugizaki/Synopsis

History
When he was a young, Soga wanted to become a hero. However, people were constantly writing him off based on his appearance, his violent behavior and dangerous quirk, rejecting and ridiculing him as if he were some monster. This caused him to develop a violent personality and be rather sensitive to people laughing at him, getting into troubles frequently.

He also used to play guitar up until he got it destroyed in a fight.

Synopsis
While he was walking with his friends Moyuru Tochi and Raputo Tokage, Koichi Haimawari unwittingly bumps into him and spills his juice. Wanting to humiliate Koichi, Soga asks him to apologize and kneel, but Koichi flees. After that, he and his friends enter a convenience store, and they encounter Koichi again. Soga becomes angry at seeing Koichi again and takes him outside to beat him. Koichi is not able to fight back because of Soga's spikes. Later that same day, Koichi and Kazuho meet the thugs in an alleyway, and the thugs recognize her as the online idol and begin mocking her. Koichi tries to stop them but gets beaten again.

Suddenly, Knuckleduster appears and defeats them with ease. Soga rises again and threatens to hurt Pop☆Step's face, but Koichi charges at him and knocks him down, allowing Pop☆Step to fly above for safety. Knuckleduster punches the thug leader into the wall which knocks him out. After that, the thugs are offered samples of Trigger from Mario Kugutsu.

The next day, after seeing Koichi and Pop☆Step chasing Mario, Soga, along with Moyuru and Raputo, uses the Trigger sample, turned into a Impromptu Villains, and attacks Koichi. But before he can do any harm, he is defeated and captured by Shota Aizawa, who is on his day off, while his teammates are also defeated and arrested.

Days later, he is released, and with Moyuru, he visits Raputo who had been in the Hospital since the experience with Trigger. Raputo says that he enjoyed the experience offered by the drug, but when Souga asks Raputo if he would be interested in taking Trigger again, Raputo says no, because although he liked that Trigger increased the capabilities of his Quirk, it is also the reason why he ended up hospitalized. He has already learned the lesson from his past experience and does not want repeated it again.

Before this, Soga decides to take his friends away from the drug, and faces Kuin Hachisuka, who had allied with Stendhal to get rid of the previous Impromptu Villains, including him and his friends. Kuin gives him the offer to inject Trigger to be able to fight against the murderous vigilante, but Soga rejects it, declaring that he will defeat him with his own abilities and without any kind of help. Faced with this refusal, Kuin frees a swarm of bees carrying Trigger and injects it to Souga by force, transforming him back into a Impromptu Villains to face Stendhal.

Koichi intervenes in the fight and tries to save Soga, by understanding that Stendhal has no intention of simply defeating him and locking him up, if not directly killing him. Koichi tries to escape taking with him a badly wounded Souga, but the Sthendal’s Quirk paralyzes them. Just as he was about to finish them, Knuckeduster appears and defeats Sthendal, saves Soga nad Koichi’s lives.

After being saved, he's hired by Knuckleduster to look into the whereabouts of his daughter and Kuin's host, Tamao, effectively making him Knuckleduster's informant. After Tamao is freed from Kuin's control, he and his friends watch over her bedside whenever Knuckleduster is out.