Soga Kugisaki/Synopsis

History
When he was a young, Soga wanted to become a Pro Hero. However, people were constantly writing him off based on his appearance, his violent behavior and his 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 trouble frequently.

He also used to play guitar up until he got the one he owned destroyed in a fight.

Vigilantes Beginnings Arc
While he is walking with his friends Moyuru Tochi and Rapt Tokage, Koichi Haimawari unwittingly bumps into him and spills his juice. Wanting to humiliate Koichi, Soga asks him to apologize by kneeling at his feet, 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 the spikes Soga produces with his Spike Quirk. Later that same day, Koichi and Kazuho Haneyama meet the thugs in an alleyway, and the thugs recognize the latter as the online idol Pop☆Step 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 a safe distance away. 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, Moyuru and Rapt, Soga uses the Trigger sample, turns into a Instant Villain, and attacks Koichi. But before he can do any harm, he is defeated and captured by Shota Aizawa, who is on his day off and just happens to be passing, while his teammates are also defeated and arrested.

Stendhal Arc
Days later, he is released. He gives a message to Ichimoku Samazu and Jube Namimaru to pass it on to Koichi and Kazuho, in which he wants to meet with them at Ichimoku's family restaurant, although without saying his identity.

Koichi and Kazuho accept the invitation but have an unpleasant surprise when they discover that it is Soga Kugizaki. Soga is disheartened by their reactions and questions why they think poorly of him, to which Kazuho replies that he tried to murder them. Soga is annoyed and sees that there is no point in talking with them, although Koichi wonders what Soga wants to talk about.

Next day he and Moyuru visit Rapt, who had been in hospital since the experience with Trigger. Rapt says that he enjoyed the experience offered by the drug, but when Soga asks Rapt if he would be interested in taking Trigger again, Rapt says no because although he liked that Trigger increased the capabilities of his Quirk, it is also the reason that he ended up hospitalized. He has already learned the lesson from his past experience and does not want it to be repeated.

Before this, Soga decides to take his friends away from the drug and is consequently forced to face Kuin Hachisuka, who had allied with Stendhal to get rid of the previous Instant 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 Soga by force, transforming him back into a Instant Villains to face Stendhal.

Koichi intervenes in the fight and tries to save Soga, understanding that Stendhal has no intention of simply defeating him and locking him up, just directly killing him. Koichi tries to escape, taking with him a badly wounded Soga, but Stendhal’s Quirk paralyzes them before he can. Just as he is about to finish them, Knuckleduster appears and defeats Stendhal, saving Soga and Koichi’s lives.

Vs. Queen Bee Arc
After being saved, he's hired by Knuckleduster to look into the whereabouts of Kuin Hachisuka, effectively making him Knuckleduster's informant. Based on the uniform she wears, Soga tracked down her middle school and once there, he shows an old picture of her, asking other girls if they know her. Even though other girls find it creepy of him to ask it in a middle school, they do notice that resembles Kuin Hachisuka as they wonder if she is in some kind of trouble.

Soga is forced to leave when the staff approach him and asks him to go away.

After walking past an alleyway, a girl from the middle school asked in the alleyway if he had business with Kuin, wondering what he would do if he found her as what he is doing seems shady. Soga informs her he is only a messenger and has no idea if it is shady or not. Then, the girl begins to behave a bit seductively,which makes Soga feel uncomfortable, who asks her to cut it out.

Suddenly, a swarm of bees that had been controlling her comes pouring out from under her skirt to attack him. Soga reacts quickly by drawing a spray of bee repellent and breaks open it with his spikes. Soga leaves the alley wrapped in bee repellent, but the swarm pursues him. The bees try to attack him, but Moyuru Tochi uses his Quirk to set them to ashes. He is seen with Rapt Tokage on a motorcycle, as lizard tells Soga to hop on. The other guys wonder about Soga's actions as they are jealous of him hogging the fun.

Later, Soga meets with Knuckleduster in a hospital entrance. He is mad that there is no one actual registered as “Kurogiwa” in the hospital. Knuckleduster states he uses that name to get in touch with people, making Soga wonder who his real name is. Despite the errands Soga had run into, Knuckleduster views him as a guy who does not pry into other people's business.

Soga reports him the little information he could get before he was attacked. He tells him what her middle school is and that she uses “Hachisuka” as a pseudonym. Knuckleduster counts the info as intel, including the fact it is a private school. Soga notices he is getting into some nasty stuff and wonders about his two other friends. Knuckleduster states there is no need to drag them into this since he used him as a bait to draw attention. Soga is not amused. Soga's friends feel he should stay away from things.

After leaving Knuckleduster, Moyuru and Rapt tell Soga that he should stay away from things. Koichi Haimawari catches up with and greets them, to which Pop Step to stay away. Moyuru notices how brave he is to talk with the people who beat him up before. Rapt tries to get a close view of Kazuho. Koichi states a lot has changed, but Soga walks away.

Sky Egg Bombing Arc
After Tamao is freed from Kuin's control, he and his friends watch over her bedside whenever Knuckleduster is out.