>>58539115Blue is your rival and also fights Team Rocket
You team up with Lance at the Lake of Rage/Mahogany Town
You run into Steven a few times and team up with him at the Space Center and some other places
Wallace helps you summon Rayquaza in Emerald and gives you the HM for Waterfall
Cynthia is repeatedly encountered and helps you against Team Galactic
Alder mentors you and Cheren throughout the game and opposes Team Plasma
Iris is a former Gym Leader and again helps you against Team Plasma
I shouldn't have to explain Leon or Nemona and I already addressed Geeta
Diantha is the only Champion in the entire franchise who does basically nothing for you or with you. But I do have a small correction, she shows up to talk with the Professor and do nothing two (2) times, not just once.