Twelve year-old Shun travelled from Brazil to Japan six months following the death of his mother. His mother's last request was for Shun to find his older brother Ryu, who had been living under the care of the martial arts master Gouken since his infancy. When he met Ryu and Ken Masters at their sensei's old dojo, they were somewhat skeptical of Shun and weren't entirely convinced by his story, but allowed him to stay with them. Over the days Shun stayed with him, Ryu developed a fledgling attachment with the boy and the two even sparred together. While not on Ryu or Ken's level, Shun was a competent fighter, though his fighting style was undisciplined. To Ryu's disturbance, Shun also demonstrated a dark streak which showed itself when the two brothers got into a fight with a bunch of street punks.
Later that day, Ryu and Shun entered a Street Fighter Tournament in Kabuki Town. Ryu didn't participate himself, but Shun fought against the Russian wrestler Zangief and almost got himself killed. During the fight, he also displayed the power of the Satsui no Hado (aka the Dark Hadou), an evil power wielded by ancient assassins that was passed down through the students of the Shotokan school where Ryu had trained. Shun explained to Ryu that he had learned the technique from their father before he abandoned him.
Professor Sadler, the mad scientist who had hosted the tournament, decided he wanted to acquire the power of the Satsui no Hado and so he had his agents kidnap Shun so he could study him. Shun's dark connection was not as strong as Ryu's, however, but Sadler knew that Ryu would likely try to rescue the boy, and so Shun served as the perfect bait to lure Ryu into a trap. Sadler hosted another Street Fighter competition at his desert laboratory and when Ryu, Ken and Chun-Li started snooping around the facility, Sadler released his Rosanov cyborg on the group. As Ryu fought Rosanov, the cyborg revealed that Shun was inside its body. The brainwashed Shun mocked Ryu and goaded him into using the Satsui no Hado to destroy him. As Ryu watched Rosanov beat his friends to near death, their attacks having no effect against it, he gave in to the murderous intent and fired of a Messatsu Gou Hadou, the only attack that could destroy the cyborg. The attack worked and Shun was blasted out of Rosanov's body.
Following Sadler's torture of him and the blow he recieved when inside Rosanov, Shun's injuries were severe. After Ryu overcame the Satsui no Hado and defeated Sadler, he knelt beside Shun and held him in his arms as Shun slipped away. Before he died, Shun asked Ryu why he came for him since he didn't even believe they were brothers. Ryu merely answered "Because you are my brother."