• English / United States: Marissa
• Japanese / Japan: マサミ
• Japanese (Romanized) / Japan: Masami
• Japanese (TL) / Japan: Masami

Marissa lives on Sunburst Island with her big brother Mateo. She helps him run a glass and crystal shop. Realizing that her brother needed the inspiration that her Grandpa once got from seeing the Crystal Onix, she decided to send out a message in a bottle to see if people would be able to help her and Mateo find it.

The letter she wrote stated: "If you know anything about a Pokémon called the Crystal Onix, let me know right away." Ash Ketchum and his friends found the bottle near Sunburst Island and then decided to help her find the Crystal Onix as Ash Ketchum said it wasn't polite to let a letter from a little girl go unanswered.

Marissa went along with everyone as they searched the Sunburst Island for the Crystal Onix. She was a bit scared when they initially found it but was happy that she was able to see it. Marissa was very grateful to Ash Ketchum and his friends for helping her and her brother find the Crystal Onix.