There should be multiple Rivals, the character you don't pick should be your childhood friend and the other one should be like Gary/Blue, a guy that grew up in the same town as you but you have always been rivals, and you should all get your starter Pokemon at the same time, also which ever Pokemon you pick the "Gary/Blue" character will pick the starter strongest against it, and the character you don't play as will get the starter weak against yours, also the "Gary/Blue" character could join the Evil team after loosing to you in the hopes of getting there revenge on you.