Marissa is a one-time character in the Pokémon Anime who premiered along side her older brothe Mateo in EP087.

Marissa has thrown a bottle in the ocean with a letter in it asking if anyone knew about the Crystal Onix and to come see her on Sunburst Island. Ash and co. happened to come across the letter and headed for the island. When they found her she was being terrorized by one of the other shop owners saying that Mateo should just close up shop. Unfortunately Ash didn't know anything about the Crystal Onix but he did offer his help.

Marissa is a sweet girl who looks up to her brother and is always willing to help him. Even though Mateo didn't believe in himself at times, she always did.

Trivia

Marissa has a hair style similar to that of Chibiusa of Sailor Moon.