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Billy Jo is a minor character appearing in Pokémon Black 2 and White 2 and the Pokémon anime. She is a member of Roxie's band, playing guitar.

Billy Jo appeared in Rocking the Virbank Gym! Part 1 and Rocking the Virbank Gym! Part 2. She is a guitarist playing with Roxie and Nicky in the band "Koffing and the Toxics", which is quite well known in Unova and provides music during Roxie's Gym Battles. When Ash came to the Virbank Gym, Roxie described Billy Jo as a "poisonous person".

She once went on tour with the band through Kanto, but mentioned to Ash that the audiences there were "a bore".

(Source: Bulbapedia)