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 also has a strong affection to Chloe, and loves her the most despite her somewhat aloof attitude. According to Parker Yamper will not accept any food unless it comes from Chloe.
Yamper first appeared where it saw Ash at Cerise Laboratory. Ash then attempted to befriend it, but Yamper electrocuted him instead, causing him to faint. Yamper quickly befriended Pikachu, before its trainer Chloe arrived and walked away. Yamper then reappears after Ash and Goh got back from their adventure with Lugia.
When Ash and Goh returned from their adventures in the Galar region, Yamper appeared when it see Goh'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 Cerise house, where it and Chloe were asleep in their room when the alarm clock rings. After breakfast, Yamper along with Chloe and Professor Cerise then head off to their Institute. arriving at the Institute, Yamper was sad from Chloe leaving for school. Yamper along with Ash and Goh encountered a mysterious Gengar at the Cerise Laboratory and starts attacking everyone. During their search for Gengar, Yamper greets Chloe after she came home from school. However, Gengar showed up and attacked them. Chloe and Yamper then battle Gengar and defeated it, causing it to leave the Institute. At night, in the Cerise 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.