Catch them in order of when he met them

Ash came to the conclusion that for nostalgia's sake, he would relive his adventures. That made his first target very clear; Misty. Misty was currently the Gym in Cerulean City, so it wouldn't be too hard for Ash to find her. Ash went back home to pack, which his mother insisted on doing instead. When Mrs. Ketchum had packed everything she thought her beloved son would need, she returned to her pokeball and left Ash and Pikachu to start their journey. Ash grabbed the pokeball his mother was in and marked it "Mom" with a black marker. He then put it on his belt, grabbed as many of the new pokeballs as he could, and headed off to Cerulean City.