Mashiro Munetani, nicknamed "Shiro," is the deputy captain and executive officer of the destroyer Harekaze. She comes from the renowned Munetani family, boasting generations of service in the Blue Mermaids starting with her great-grandmother. Her mother, Mayuki Munetani, is principal of Yokosuka Girls' Marine High School and a former Blue Mermaid captain. Mashiro's older sisters also serve prominently: Mashimo as supreme commander of the Blue Mermaids' Japan branch and Mafuyu as captain of the advanced vessel "Benten." This legacy burdens Mashiro with intense pressure to uphold the family tradition, driving her determination to become a Blue Mermaid herself. Mashiro has a light complexion, thigh-length dark brown hair usually in a ponytail, and distinctive family red eyes. Her uniform features a gold aiguillette signifying her rank. Notably confident when temporarily commanding the Harekaze, she let her hair down. Academically, she excels across all subjects, particularly gunnery and torpedo operations, holding certifications like Level 2 Maritime Technician and basic waterway traffic control. Despite her competence, she frequently experiences misfortune, encapsulated by her catchphrase, "I'm so unlucky." This trait began when wind blew away her mother's hat, gifted as encouragement, marking the start of her perceived lifelong streak of bad luck. Her assignment as deputy captain resulted from an exam error where she misplaced her answers, landing her on the Harekaze instead of a more prestigious ship. The role requires enforcing decorum, often clashing with Captain Akeno Misaki's unorthodox, impulsive style. Initially, Mashiro serves as a strict, by-the-book counterbalance, openly criticizing actions like abandoning command during crises. Her disciplined approach earns admiration from peers like assistant engineer Hiromi Kuroki, who sees her as more suited for captaincy. Mashiro suffers from ailurophobia (fear of cats), stemming from a childhood incident where a kitten she cared for vanished. This phobia surfaces with the Harekaze's cat, Isoroku. She overcomes it after being trapped aboard the sinking merchant ship Shinbashi with a kitten named Tamonmaru. Their shared isolation and her rescue efforts gradually alleviate her fear, marking significant emotional growth. This experience, coupled with Akeno’s unwavering trust during rescues, reshapes her perspective; she adopts the motto, "All misfortune is but a stepping-stone to the future," reflecting her evolving resilience. Her character develops through joint operations. Initially frustrated by Akeno’s risk-taking, she gradually accepts its effectiveness, notably supporting Akeno during the Musashi rescue when Akeno hesitates. Later, she faces a personal crossroads when offered captaincy of the destroyer Hiei during an inter-school competition. Struggling with this decision strains her relationship with Akeno and costs their team a race victory. She postpones her choice to focus on an anti-piracy mission, where she commandeers a skipper boat to blast debris blocking the Harekaze’s escape from a collapsing seafort. After this decisive leadership act, she resolves to become a captain someday but chooses to remain on the Harekaze for now. Mashiro enjoys flounder sashimi and collects stuffed animals, her favorite being a shark named Bruce. She dislikes Korean-style marinated ribs (kalbi). Her hobbies include swimming and checking horoscopes. Her height was initially 159 cm but adjusted to 160 cm in the 2020 film. She maintains a close, evolving friendship with Kouko Nosa, who calls her a "friend of the heart."