Masa is a supporting character in the anime Stitch! and a member of Piko's entourage. He is often seen alongside Koji and Taka, acting as one of Piko's followers. In the English adaptation of the series, he is renamed Marvin. Masa has a light brown skin tone and black hair, with an oval face that gives him a slightly tanned appearance. He typically wears a yellow shirt with blue sleeves and tan shorts, and he sports an orange bracelet on his right wrist.

Masa's background places him as a student of Combat Karate, though his skills are unimpressive. He tends to go along with Piko's selfish and demanding nature, getting along well with her despite her bossy attitude. His primary motivation appears to be fitting in with his group and gaining approval from Piko, often by bullying or provoking others. He once called Jun a weak guy and challenged him, but he was easily defeated in a fight, leading Piko, Koji, and Taka to mock him as sloppy. This incident highlights his lack of real strength or competence.

In the story, Masa functions as a minor antagonist, part of the group that bullies Yuna and her friends. He does not have any significant character development or growth throughout the series; he remains a follower who tries to appear tough but is ultimately ineffectual. His key relationships are with Piko, whom he obeys, and with Koji and Taka, his fellow lackeys. He also interacts with Jun, whom he antagonizes but fails to intimidate. Masa possesses no notable abilities beyond being a mediocre karate student, and his poor performance in combat underscores his role as a comic-relief bully.