Now that I have your attention w/ onions boy rival, here's an idea for a GOOD rival:

Rival starts off friendly, but is pretty competitive, and as you keep winning against him he starts to resent you a bit. Once the evil team starts becoming relevant, you don't see him around anymore, but as you're going through the evil team's base/place they took over, you find him as a grunt you just randomly encounter in the middle of everything. He notices you, and once you beat him he tries to convince you to join the team because people have the wrong impression of them etc. Obvs it would be cool if they gave you the option to join but if not then whatever

Then, once you face the team boss, he notices that your rival knows you and makes him fight against you as a test of loyalty or something. When you win, the boss ditches the rival and he goes off somewhere else.

At Pokemon league, you encounter him with a team of much friendlier Pokemon leveled up to be on-par with the E4's levels

Thoughts?