Yamper is friendly, as he befriends Pikachu whom he met at first sight. However, he 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 also hates receiving affection from those who aren't Chloe as shown when he electrocuted Ash in "Legend? Go! Friends? Go!", which ruined his overall impression of him.
It is also worth noting yhat Yamper gets jealous easily, as shown in "There's a New Kid in Town!" when a Trainer's Pidove was being fond of Chloe.
Yamper was originally given to Prof. Cerise by one of his friends who lived in the Galar region. He was then introduced to Chloe, and became very excited to meet her. However, his enthusiasm ended up scaring the then very young girl, and she ended up crying. Yamper continued to try and play with Chloe, but she eventually told him to get lost. Obeying her despite her not liking it, he decided to run away. Yamper was very happy to see that Chloe had gone looking for him afterwards, and protected her when she was cornered by a group of Venonat. Because of this, they started to sleep in the same bed and Yamper started to accept food only from Chloe.
Yamper first appeared where he saw Ash at Cerise Laboratory. Ash then attempted to befriend him, but Yamper electrocuted him instead, causing him to faint. Yamper quickly befriended Pikachu, before his 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 he see Goh's Scorbunny, and starts chasing it around until he was greeted by his friend Pikachu as they play with each other while they ignored Scorbunny.
Yamper was at 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.
When a Pidove started living at the Cerise household due to being injured, Chloe began to take care of it out of her own time, causing Yamper to become very jealous. Yamper kept trying to get Chloe's attention, but she would keep taking care of Pidove. Eventually, when they were attacked by a Fearow, Chloe and Yamper became in-sync again after Chloe had Yamper use Spark on Fearow, driving it away. When Pidove ended up leaving, Yamper said his goodbyes.
- 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.