Giselle is a student at Pokémon Tech, a trainer school located between Cerulean City and Vermilion City. She's best known for her appearance in the anime episode "The School of Hard Knocks," where she served as the antagonist.
At Pokémon Tech, Giselle was popular and experienced—but she used that status to bully younger and less skilled students under the pretense of tutoring them. When she confronted Joe after his loss to Misty, her cruelty became obvious. Misty called her out on it and challenged her to a battle, only to lose against Giselle's Graveler despite having the type advantage with her Starmie.
That loss sparked a chain reaction. Ash got fed up with Giselle's smug attitude and her dismissal of friendship-based training. She mocked him for being on the road only two months with just two badges and three Pokémon, and she especially went off about how Pikachu were terrible starter Pokémon—little more than pets for kids. Naturally, Ash and Pikachu were furious and demanded a rematch.
The battle turned out to be Giselle's wake-up call. Locked out of using Electric moves, Pikachu went feral with physical attacks—biting, scratching, the works—before trapping Cubone's vision with its own skull and letting Cubone knock itself out with its own Bonemerang. Giselle lost and finally admitted that real training can't come from books alone.
When Team Rocket attacked the school afterward, Giselle rallied the students to drive them off. She and Joe reconciled, and he decided to leave and pursue badges for the Pokémon League.
Giselle also appears in the Electric Tale of Pikachu manga as a trainer traveling Kanto and collecting strong Pokémon, including at least one scene alongside Joe.
Content compiled by AnimeList.moe from publicly available sources.
