Kay

Kay is a character of the day who appeared in Stage Fight!.

Kay was a member of the Pokémon Showboat, a group of performers who provide voices of Pokémon while the Pokémon act in a show. While all of the other actors in the show got along with their Pokémon, Kay didn't get along with her Raichu.

She revealed to Ash that the reason she and Raichu didn't like each other is because of something that happened when they first met. Raichu was so happy, it jumped into Kay's arms and used Thunder Shock. Frightened, Kay accidentally threw Raichu, and the Pokémon became frightened of her. From then on, Raichu sensed that Kay was nervous around it and thus was nervous around her as well.

Kay and Raichu finally gained each other's trust during a battle with Team Rocket. Kay, providing Raichu's "voice," was able to distract Team Rocket and send them blasting off.

(Source: Bulbapedia)