Sid was among the five founding members of the gang Bison, joining alongside Riki and Guy. He projected a firm, reliable presence, speaking sparingly yet holding his ground without provocation. However, his demeanor could shift to fierce confrontation during bad moods. Sid frequently restrained fellow Bison members, particularly Luke, guided by his personal conviction that intelligence outweighed brute force for success.

Longstanding romantic feelings for Riki likely drew Sid to Bison initially. Instead of acting on them, he channeled these emotions into unwavering admiration and loyalty toward Riki's leadership. Privately, he resented Guy's exclusive partnership with Riki, though he suppressed these thoughts entirely. Sid vehemently opposed any threat to Riki, confronting Luke once with a stern warning over a suggested assault.

His loyalty encompassed the entire gang, and he mourned deeply when Riki first vanished. After Riki’s return and subsequent second disappearance, Sid dedicated extensive time and resources to finding him. Discovering Riki’s enslavement by Iason, and the secrecy between Riki and Guy, struck him profoundly.

Sid had a prior entanglement with Kirie, who targeted him to infiltrate Bison. Sid championed Kirie’s membership partly due to Kirie’s resemblance to Riki. Kirie routinely manipulated Sid through sexual overtures to sway other gang members, exploiting Sid’s influence. Though Sid tolerated Kirie more than others, he acknowledged Kirie’s irritations and often joined in teasing him.