Masu Tsunajima, commonly addressed as Masu-san, fulfills the role of cook aboard the space pirate ship Arcadia. She appears as an elderly woman with gray hair typically bound in a bun, circular glasses resting near her mouth, and eyes set high on her forehead. Her standard outfit comprises a shirt, vest, skirt, and apron.

Her demeanor merges cheerfulness with fierce protectiveness over her kitchen. She reacts violently to ingredient thieves—especially Doctor Zero and his cat Mi-kun during their raids—by brandishing knives, serving as comic relief. Dedication to culinary duties defines her, though crew members never explicitly assess her cooking quality.

A significant personal history involves a failed engagement to Gozo Otowara. Circumstances prevented their marriage, leading her to believe he abandoned her. Years later, she learned external factors caused his absence, not intentional desertion. They reconciled briefly through communication shortly before Mazone aliens killed Gozo. Following his death, the alien crew member Miime consoled her using empathic abilities.

Her role remains consistent across appearances. In the original 1978 *Space Pirate Captain Harlock* television series, she manages the galley and engages in recurring skirmishes with Doctor Zero over his sake theft and his cat’s food raids. She reprises this position in the *Endless Odyssey* OVA series without altered characteristics or expanded backstory. She does not feature in the *Harlock Saga* OVA, the 2013 film adaptation, or the *Dimensional Voyage* manga.

Key relationships emerge aboard the Arcadia. She maintains a contentious dynamic with Doctor Zero over his kitchen intrusions and sake consumption. Conversely, she shares a bond with Miime that extends beyond crew duties, evidenced by Miime’s emotional support after Gozo’s death. No official family ties or personal developments beyond her engagement history are documented.