While Heather was exploring, she accidentally fell into a lake. She couldn't get onto dry land, but suddenly a wild Mudkip came and rescued her. They became friends, as Mudkip took care of Heather. Mudkip decided to be in Heather's journeys with her. Mudkip is her main Pokémon - and they haven't been separated since!
While Heather was camping, she stumbled across a wild Pikachu. It kept following her, which annoyed Heather. She decided to battle the wild Pikachu. They became friends, but a rivalry grew between her Mudkip and Pikachu. Heather captured it, becoming one of her best friends.
Heather found Eevee weak while she was exploring. She took it to the nearest Pokémon Center, which revived the poor Eevee. They became friends, with Eevee going along with Heather. They became best friends afterwards.