Tierno debuted in Summer of Discovery! along with Shauna and Trevor, and his Squirtle. He first had a battle against a Trainer's Conkeldurr and won. Later that episode, he battled Ash's Froakie. During his battle with Ash, he revealed that he dreams of forming a dance unit with his Pokémon.
In Foggy Pokémon Orienteering!, Tierno, along with Trevor and Shauna, decided to put the race on hold to help Ash, Serena, and Clemont find Bonnie. The group later encountered a mysterious Pokémon with an X mark on their way back to the camp. Although they arrived too late at the camp to win any points in the race, they declared that helping their friends was totally worth it.
In Battling Into the Hall of Fame!, Shauna, Tierno, and Trevor participated in a Team Battle withBulbasaur, Squirtle, and Charmander, respectively. Their opponents were their new friends and rivals, Ash, Serena, and Clemont and their respective starter Pokémon. Tierno is the last to defeated in the battle, where his Squirtle is defeated by Ash's Pikachu.
He also was seen in a flashback in Showdown at the Shalour Gym!.
He appeared again in Good Friends, Great Training!, Tierno meets Ash during their journey to the Lumiose Gym, he reveals already have had their challenge there, and which also he got the Voltage Badge in a battle against Clembot. Soon after, Tierno reveals the Pokémon that he caught after the camp: Hitmontop, Ludicolo, Politoed and Raichu.
Both decide to have a Pokémon battle, however it's interrupted by Team Rocket which capture Ash's Sliggoo and Raichu and Wartortle of Tierno. After the group separating, Tierno and Bonnie meet with the lost Pokémon and decide to go help Ash and Serena. During the confrontation with Team Rocket, Tierno witness the evolution of Sliggoo into Goodra and defeating Jessie and James's Pokémon easily. Later, he battled Ash with his Wartortle and Raichu, who were defeated by Goodra and Pikachu.
He appeared again in Performing with Fiery Charm! where he watched Serena competing in the Dendemille Town Pokémon Showcase along with Shauna and Trevor.
Tierno met Ash and his friends again in Tag Team Inspiration, where he was accompanying Shauna at the Pokémon Showcase that would be held in Anistar City. He revealed that his Wartortle had evolved into a Blastoise and that he had tried to battle at the Gym of the city but lost to the Psychic-type Pokémon from the Gym Leader. Later, Tierno and Ash had a Tag Battle with Serena and Shauna which was eventually called off without any Pokémon getting defeated. He then had a battle again only with Ash, but the winner is not shown. He and Shauna remained in the group, with Tierno that assisted the Pokémon Showcase, which Shauna and Serena participated in, that happened in the next episode alongside Ash, Clemont and Bonnie.
This listing is of the Badges Tierno has obtained:
- Voltage Badge (prior to A Fork in the Road! A Parting of the Ways!)
- Pokémon Summer Camp - Runner-up (with Shauna and Trevor; Battling Into the Hall of Fame!)