Rapt and Moyuru are Soga's best friends, having a strong feeling of loyalty between them. Almost always he is usually with them, and they usually commit their misdeeds together. Despite his violent and antisocial nature, Soga cares towards them, such as when he went to face Kuin alone and warned her to leave his friends out of their conflict.
Although Soga wants to keep Rapt and Moyuru out of dangerous situations, they care in the same way for him, so they always help him when he has the chance. A proof of the friendship between them is when Soga decided to rescue Kazuho from the Queen Bee's influence, he gave them the option of not getting involved, as they would have to break many laws to save her. Rapt and Moyuru decided to help despite the consequences
At first, Soga hated Koichi, thinking he was another one of those people who mock and laugh at him of him. When Koichi accidentally spilled his juice, Soga demands him humiliate himself as an apology, to which he refuse and flees, although later Soga would beat him up. When he and his friends assault Kazuho, Koichi and Knuckleduster defeat them. In revenge, Soga acquires Trigger and turned into a Instant Villain, violently attacking Koichi, although Shota Aizawa stopped him before he hurt someone and sent him to prison.
After this incident, Soga's behavior began to change, and although he no longer had a desire for revenge, Koichi did not trust him at all. Their relationship begins to improve after Koichi risked his life to protect his from Stendhal. Although he does not recognize it, he is grateful for it, and even begins to show certain signs that he also cares for him.
Over time, Soga becomes one of Koichi's greatest allies, rescuing him after being defeated by Bee☆Pop and taking care of him along with Rapt and Moyuru until he recovered, shortly after helping him rescue Kazuho from the control of the Queen Bee.
When Soga met Kazuho in person, under her Pop Step persona, he and his friends made fun of her and tried to assault her, which is why Kazuho hates him. After the incident with Stendhal, she treated his injuries and their relationship improves slightly, although unlike Koichi, she finds it harder to accept Soga, as she still does not forgive him for what he tried to do to her and does not hesitate to insult him. Soga, on the other hand, simply ignores her.
With his change of attitude for the better over the years, and despite her antipathy that she professed towards him, upon discovering that Kazuho is being controlled by the Queen Bee, Soga is willing to do anything to save her.
After Knuckleduster gave him a beating while helping Koichi and Kazuho, Soga hated him and wanted to take revenge on him. But after he saved his life when Stendhal tried to kill him, their relationship changes completely.
After being saved, he's hired by Knuckleduster to look into the whereabouts of his daughter and Kuin's host, Tamao Oguro, 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.
Knuckleduster came to trust Soga so much that he even reveals things he keeps hidden from his Koichi and Kazuho, such as the warehouse he uses as a secret base. Shortly before Knuckleduster disappeared, he asked Soga to keep an eye on Koichi and Kazuho, and handed him a letter to give to Koichi in case they ever had trouble. Soga keeps his promise, and as a sign of respect for old Vigilante, he begins to wear a trench coat similar to his.
While he was occupying Tamao's body, Kuin sends Stendhal to kill Soga and his friends, although she tries to manipulate Soga so that he injects a dose of Trigger to have a chance against the murderous vigilante. But when Soga refuses, Kuin injects the drug to him by force, turning it into a monster.
After being saved by the Naruhata Vigilantes, Soga helps Knuckleduster to find Kuin, and when Tamao is released from Kuin's control, Soga and his friends take care of her in the hospital. Soga seems to get along with Tamao Oguro, sharing a passion for music. Soga tunes her guitar and encourages Tamao to play it, which causes Rapt and Moyuru to tease him and call him a sweetheart, much to his annoyance.
- My Hero Academia: Vigilantes Manga: Chapter 76.
- My Hero Academia: Vigilantes Manga: Chapter 1.
- My Hero Academia: Vigilantes Manga: Chapter 11.
- My Hero Academia: Vigilantes Manga: Chapter 75.
- My Hero Academia: Vigilantes Manga: Chapter 19.
- My Hero Academia: Vigilantes Manga: Chapter 28.
- My Hero Academia: Vigilantes Manga: Chapter 10.
- My Hero Academia: Vigilantes Manga: Chapter 45.