Yeah, no. He's actually a creepy sociopath who trusts only himself, having lived the past twelve years in constant fear for his life.

His father is Yutaka Kazami.

Souta is actually the son of Yutaka Kazami. When his father lost his sense of taste, he would taste his candy for him, to let him know it was all right. But the night before Kazami's biggest competition, Naitou attacked and restrained Souta, so that he wouldn't be able to help his father win. Trapped in a car in the snow for several hours, Souta was consumed with fear, anger, and shock, to the point where he suffered partial memory loss over the event. By the time he was coincidentally rescued by Ryouken, he was barley the same kid anymore.

Souta spent the next six years in an orphanage with Naitou. His memory came back to him but in pieces: he mistakenly believed that it was Naitou's father that murdered his, as a result of Naitou trapping him. Still he pretended to be Naitou's friend. One night, he was outside when the orphanage was visited by President Teikun Ou of Zheng Fa. He hid in a play structure, and witnessed Teikun's assassination at the hands of Ryouken and his accomplices. As Bansai, Marie, and Teikun's double disposed of the body, Souta overheard them discussing plans to murder Ryouken, as they considered him a loose end. Because Souta recognized Ryouken as the man that had saved him from the frozen car, he snuck over to Ryouken and revealed their plans. He set a small fire at the orphanage to cover Ryouken's tracks, and the two of them escaped together.

For years after that, Souta lived in fear. He knew from the news that Bansai and Marie had gotten away scot-free with their assassination, and the two of them quickly rose in stature. The doppelganger, too, became the president of Zheng Fa. Souta was sure that they meant to kill him just as they planned to kill Ryouken. He trained to live up to the standards of his surrogate father, Ryouken, and kept in contact with him even after he was caught and imprisoned. But when Teikun announced his return to Japan, Souta knew he had to act if he was going to get his enemies before they caught up to him. He hired Shelly de Killer to kill Teikun's double, and embarked on an elaborate plot to get Naitou, Bansai, and Marie behind bars or (even better!) killed.

Shuuji tried for weeks to escape, by digging a hole from his cell to the detention center. But when he saw his opening, he was thwarted by his own pet polar bear, Mark.

But Marie's "home" was changed forever when former assassin Ryouken was transferred to her prison. He immediately began threatening her, insisting that she provide him with special items and favors, or else he would target her and her family using his subordinates still running free. Marie bowed to his whims, while at the same time tried to help the police catch Ryouken's "dogs" in order to free herself from his influence. But Ryouken never gave up anything in their interrogations. When Naitou was admitted to the prison with a concealed weapon she assumed he was one of Ryouken's goons sent to kill her, and in a panic, she turned on him first, killing him. Then, making the best of her situation, she tried to frame Ryouken for the murder in the hope that he would at least get transferred to another prison and leave her alone.

Of course, the bad blood between Ryouken and Marie goes back further than that. Years ago, Marie owned an orphanage (the same orphanage where Naitou and Souta spent several years). 12 years pre-game she was approached by Teikun's body-double, and was enlisted in a plot to kill Teikun himself. She agreed, and after Ryouken carried out the assassination itself, she and Bansai buried the body near the orphanage. Fearing that Ryouken "knew too much" they planned to kill him, too, but those plans were thwarted with interference from Souta.

During the investigation that followed, Marie was arrested as a suspect, but was ultimately acquitted thanks to Bansai's influence as prosecutor. He helped her get her position as a prison warden, and for years she thought she was safe, until Ryouken himself showed up on her doorstep.