Yamper is friendly, as it befriends Pikachu whom it met at first sight. However, it can be bashful and defensive, and won't be nice to those it considers as strangers or threats.
Yamper first appeared where it saw Ash at Sakuragi Institute. Ash then attempted to befriend it, but Yamper electrocuted him instead, causing him to faint. Yamper quickly befriended Pikachu, before its trainer Koharu arrived and walked away. Yamper then reappears after Ash and Go got back from their adventure with Lugia.
When Ash and Go returned from their adventures in the Galar region, Yamper appeared when it see Go's Scorbunny, and starts chasing it around until it was greeted by his friend Pikachu as they play with each other while they ignored Scorbunny.
Yamper was at the the Sakuragi house, where it and Koharu were asleep in their room when the alarm clock rings. After breakfast, Yamper along with Koharu and Professor Sakuragi then head off to their Institute. arriving at the Institute, Yamper was sad from Koharu leaving for school. Yamper along with Ash and Go encountered a mysterious Gengar at the Sakuragi Institute and starts attacking everyone. During their search for Gengar, Yamper greets Koharu after she came home from school. However, Gengar showed up and attacked them. Koharu and Yamper then battle Gengar and defeated it, causing it to leave the Institute. At night, in the Sakuragi house, Yamper was praised by its trainer for saving her as they sleep together in their room.
- Yamper is the first secondary major electric-type Pokémon owned by one of Ash’s friends who isn't part of Pikachu family.
- Yamper is the first Galarian Pokémon who is owned by a main character.