He's the poster boy, but rarely ever the main character. With 2 it's everyone, Alpha he has a B plot and gets to be the magical macguffin in Charlie/Guile/Chin-Li's A plot, 3 is Alex/everyone again, 4 is Abel/Juri, 5 is Rashid/F.AN.G.
He's so irrelevant to the story of Bison (and really 90% of the cast) that when he fought Bison in the SFV story mode, I actually had to ask myself if Ryu even knows who Bison is. Because the only other time they had any interaction irrc is the first WW tournament and when Bison kidnapped him as a plot device in Charlie's Alpha story.