Yamper is friendly, as it befriends Pikachu whom it met at first sight.
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.
- Yamper is the first secondary major electric-type Pokémon owned by one of Ash’s friends who isn’t part of Pikachu family.