River Marque filled the role of backup pilot for Team Satomi, chafing at his limited racing chances while benched. This frustration erupted in clashes with Takeshi Jin, including one where he shoved Takeshi into a security machine, landing them both locked inside a hangar overnight.

Offered the defender position within Team Satomi, River refused, aiming solely for the forward role. After this rejection, he exited Team Satomi to become the new forward for rival Team Sledge Mamma. This move positioned him to race directly against Takeshi, driven by a desire to shift their antagonism into pure competition.

Away from the track, River maintained a generally relaxed attitude. During races, however, he displayed fierce focus and determination, channeling his energy into besting Takeshi. His intimate knowledge of Takeshi's piloting style and tactics became a key asset for Team Sledge Mamma.

The rivalry between River and Takeshi underwent significant evolution. Starting from contention, repeated on-track battles gradually fostered mutual respect. Though they remained fierce opponents during competition, their off-track interactions became increasingly cordial, evolving towards camaraderie and friendship. This transformation marked River's character journey throughout his time in the Immortal Grand Prix.