We Won

Dawn, after her journey with Ash, she spotted a Pikachu in the Wild, remains her how she and Piplup meet Pikachu, so spend time and after another Ariados incident, this Pikachu save her and her Pokémon, forcing them away, so he decided to come along, and during next Pokémon contest, they won together.

Full credit to @flav0noid on Twitter