Shun is a short child with pale skin and brown hair. His eyes have a distant look to them. When he taps into Satsui no Hado, his appearance becomes sinister, and his body is covered in a dark aura.
Shun appears to be a quiet and distant child from appearance, but deep down he's energetic and excited when it comes to fighting. His inner strength and energy comes from the experiments performed on him by Sadler.
Shun was a young boy who claimed to be looking for his elder brother: Ryu. Shun was taken care of by his mother in Brazil until she fell ill. Shun claimed that her last words were for him to search for his elder brother, whom he carried a photo of. He eventually located Ryu in Japan and was shown eager to participate in the Street Fighter tournament. Shun surprised Ryu, however, by proving to be a violent and a ruthless fighter who possesses the Satsui no Hado when fighting.
During the tournament, Shun was outmatched and seemingly paralyzed after getting bear hugged by Zangief. Ryu tried to save his brother but the crew of Sadler captured Shun alive before he could. Ryu's guilt and sadness grew into a strong anger. Days later with the help of Chun-Li, Ryu decided to enter Sadler's tournament with a group of fighters; Adon, Birdie, Guy, Dan, Rolento, Sodom, Dhalsim, his close friend Ken, and Chun-Li.
Shun was revealed to have been inserted into a powerful cybernetic body, which he used to clash with Ryu and the other fighters. He was eventually purged from it following a battle with Ryu. Later, once the battle with Sadler had ended. Ryu approached the dying Shun. Shun questioned why Ryu would come for him, not only due to his knowledge that it had been a trap, but also due to the fact Ryu never believed they had been brothers. Ryu assured him that they were brothers, a statement which seemed to please Shun. Before he died, he admitted that he had only done what he did to become strong and to get money to help his mother.