While on his way to Indigo Plateau, Ash was stopped by Otoshi, who challenged him to a battle, but with a twist: whoever lost had to give up their Badges to the winner. Ash, confident he would win, accepted the challenge. Otoshi's Marowak successfully defeated Ash's Bulbasaur, but it lost to Pikachu.
Otoshi then admitted that he had no Badges to give to Ash. Ash thought that Otoshi was a cheater, but the defeated Trainer told the story of how his Badges were stolen by somebody who he didn't know. He claimed a talking Meowth did it. Ash and his friends realized that Jessie, James and Meowth of Team Rocket must have been the ones who robbed Otoshi. Feeling sorry for him, Ash and the others decided to help Otoshi retrieve his Badges from Team Rocket.
After finding James and Meowth—who claimed that Jessie had taken the Badges from them—Marowak left Otoshi, saying that if Otoshi were a more responsible Trainer, he would never have lost the Badges and would be able to compete in the Pokémon League. Otoshi was saddened, but continued to look for his Badges.
After Ash, Misty, Brock, and Otoshi found Jessie and confronted Team Rocket, Otoshi challenged Jessie for the Badges. She told Otoshi that if he defeated her, she would give his Badges back. Using his Doduo, he tried to defeat Jessie's Arbok, but the two heads ended up fighting with each other. Just as Jessie was about to capture the Doduo, Marowak returned to Otoshi and helped him defeat Team Rocket. Marowak, who was originally angry, had seen other Trainers training alongside their Pokémon and remembered the camaraderie formed between him and Otoshi.
Otoshi, now reunited with both Marowak and his Badges, continued to Indigo Plateau to compete in the Pokémon League.