Bruno/Anime/Main series

Bruno appeared in To Master the Onixpected!. While was preparing for the Indigo Plateau Conference, he found out that Bruno was  at Mt. Hideaway near Pallet Town. was enthusiastic about the prospect of meeting Bruno, believing that he possessed some kind of secret technique that was the key to his success, so Ash, Brock, and headed out to meet him. Along the way, they learned that Mt. Hideaway was the home of a larger-than-usual.

After Bruno saved from the giant Onix, Ash and Brock begged him to take them on as students. Bruno agreed, under the condition that Ash and Brock would do anything he said. Bruno then had them chop wood, carry water, and carve chopsticks, among other chores. During this "training", Misty began to suspect that Bruno was a phony.

Not wanting to believe that Bruno didn't have any kind of special talent, Brock decided to prove Bruno's power by surprising him with a sneak attack. He assumed that Bruno's reflexes would be so amazing, he would stop Brock with ease. However, this did not happen, and Brock nearly ended up knocking Bruno unconscious. Bruno admitted that he didn't know any secret techniques on how to train Pokémon and just wanted to have someone to do a myriad of chores for him, thus shattering Brock's image of him.

Later, the group was again chased by the giant Onix. With his athletic skills, Bruno was able to save Ash from being hit by it, and then tricked the Onix into knocking itself on the head with its own tail. Once Onix was calmed down, Bruno was able to examine it, and discovered that the reason for Onix's aggressive behavior had been a stuck in-between its boulders. After Bruno removed the Sandslash, Onix became so grateful that it willingly let itself be by him. Bruno then told the group that the only true secret behind Pokémon training is that Trainers and their Pokémon should care for each other.