Rui Ōkubo competes for the Mizumoto High School soccer team, functioning as a supporting presence within the team's dynamics alongside central figures Teppei Sakamoto and Keisuke Honda. His role unfolds against the backdrop of the team's drive to transcend its legacy as a historically weak regional contender and secure competitive success.

Advancing into the sequel narrative, Ōkubo shifts from high school competition to the professional soccer sphere. This developmental phase engages him in elite international contests, specifically qualification pathways and preparatory matches en route to the FIFA World Cup 2014 in Brazil. His trajectory converges with the team's overarching ambition of representing Japan globally, signifying a marked progression from domestic high school matches to top-tier international competition.

Ōkubo’s background and growth remain consistently depicted throughout the narrative, paralleling the collective ascent of the Mizumoto team members through multiple competitive echelons toward professional careers and international opportunities.