Sean is a half-Brazilian, half-Japanese boy from a middle-income family in San Pauolo Brazil. He happened one day to witness the Street Fighter Ken Masters in a fight with local legend Jimmy "Blanka." Impressed and inspired by Ken, he hit the road in search of him, seeking to become his student. Encountering many on his journey, he learned of another fighter named Dan Hibiki whom he was often compared to.

By the time of the third Street Fighter tournament, Sean had found Ken and incessantly begged and pleaded with Ken to train him in the martial arts. Ken reluctantly took him around wherever he fought so he could observe, but he refused to train him. Sean only learned by observing Ken, and dreamed of creating his own unique style. But Sean was captured by Gill's organization, as they were going to use him firstly as another super-soldier test subject, and secondly, as bait to lure Ken into a trap. Ken ended up once again ensnared in a deadly game by the organization controlled by the malevolent being called Gill, and was locked in mystical combat with Gill's brother Urien as a helpless Sean watched. As the two battled, Chun Li appeared and freed Sean. He rushed to aid Ken, but Chun Li stopped him. She told him that Ken could take care of himself, and he should let him handle it. After it was over and Ken had defeated Urien, Ken simply told Sean that if he wanted to be the best, he should seek out Ryu, and attempt to defeat him. And so Sean sought out, and eventually fought, Ryu. But Ryu defeated him easily, time again and again. Sean realized that he would need more training if he ever hoped to defeat Ryu.