Mashū Akoya is a fifteen-year-old girl who serves as a gunner and observation officer aboard the commercial warship Pascal Magi in the anime Tactical Roar. She is the twin sister of Manatsu Akoya, and the two share a close bond, frequently working together during combat operations. Mashū has long blonde hair that she typically wears down, distinguishing her from her sister who wears pigtails, and blue eyes. Her role on the ship involves running the observation station, monitoring the vessel's surroundings and relaying tactical information during engagements.

Mashū and her sister both enjoy combat and take pleasure in playing tricks on others, a playful and mischievous personality trait that extends to their interactions with fellow crew members. The twins share many common habits, including using the same cosmetics, which underscores their strong sisterly connection. While Mashū is not a central protagonist, she is a consistent supporting presence throughout the series, contributing to the ship's defense and the crew's camaraderie. Her motivations are primarily grounded in her enjoyment of battle and her loyalty to the Pascal Magi crew, with no deeper personal arc or notable character development depicted in the available material. No special abilities beyond standard gunnery and observation duties are described; her competence in these areas, combined with her energetic and trickster nature, defines her contribution to the story. Her key relationship is with her twin sister Manatsu, with whom she shares a playful rivalry and seamless teamwork, and she interacts amiably with the rest of the predominantly female crew.