Kasumi is a Gym Leader of Hanada City's Gym, known officially as the Hanada Gym. She gives the Cascade Badge to Trainers who defeat her in battle. She specializes in Water-type Pokémon.

Kasumi is a friend and former traveling partner of the anime's main character, Satoshi. After he stole her bike and proceeded to accidentally destroy it, Kasumi followed him around the Kanto region, the Orange Islands, and the Johto region, using the time she spent with him to further her goal of becoming the greatest Water Pokémon Master.