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 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.