The moment she saw Buneary in the episode Setting The World On Its Buneary she was determined to catch her due her cuteness, but failed due her lack of knowledge. At the end Buneary expressed its crush towards Ash's Pikachu with her strange behavior towards him. Dawn managed the catch the Pokémon and Buneary was more than willing to go knowing she would travel with Pikachu by her side.
Ever since then, Dawn's Buneary was used a lot in the Pokémon Contests as well as in battle. As time went on, Buneary appeared to lose her romantic feelings for Pikachu. Despite her small size, Buneary was surprisingly powerful and was often used in battle as well as in contests.
In BW088, she is pleased to see Pikachu again and Oshawott is suprised when Buneary goes for Pikachu instead of him, due to Ash's Oshawott having a crush on Buneary.
In "Hold the Phione!", a Phione had a crush on Buneary and saw Pikachu as a rival, but Pikachu wouldn't battle against Phione for Buneary's heart, so Buneary took the challenge against Phione. If Phione had won, she would have gone on a date with it down by the ocean side. Buneary seemed to worry for Pikachu, because Phione was angry on Pikachu. After defeat, Phione swam back to ocean and Buneary felt sorry for Phione and asked it for a another battle someday and Phione accepted. That means Buneary still loved Pikachu.