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! Phione has a crush on Buneary and see Pikachu as a rival, but Pikachu won't battle against Phione for Buneary's heart, so Buneary takes challenge against Phione at If Phione wins, she'll go on a date with it down by the ocean side. Buneary seems to worried for Pikachu at Phione is mad on Pikachu.
In Memories are Made of Bliss! is never last between Buneary and Pikachu