Tsugumi Yagi, nicknamed Tsugu-chan, is the telegraph operator aboard the destroyer Harekaze, renowned for her adept communication skills and preference for smartphone typing over handwritten logs. She sports brown hair in a braid fastened with a red bow and wears the standard Yokosuka Girls' Marine High School uniform. Born on January 28 as an Aquarius with blood type O, she stands 151 cm tall. Her family oversees Suwa Shrine in Yokosuka, where she actively serves as a shrine maiden; this location holds emotional significance for crewmate Mashiro Munetani, who lost her mother’s captain hat there. Tsugumi’s mother works as a barber.

Skilled in dowsing, she discovered an oil field in elementary school and a hot spring in middle school, earning a reputation for extraordinary luck akin to fortunate ship captains. This ability guided her enrollment at Yokosuka Girls’ Marine High School after it signaled her destined path. Academically, she excels in physics but struggles with social studies, holding certifications as a Third-Class Maritime Radio Operator and Weather Forecaster to support naval operations.

Curious and energetic, Tsugumi displays a distinctive worldview that often surprises peers, maintaining a cheerful demeanor that labels her the "mysterious girl." She enjoys reading e-books, savoring sweet foods like amazake and konpeito, dislikes konjac, and favors the color yellow. During missions, she frequently partners with Megumi Uda and shares a bond with Rin Shiretoko through shrine duties; they jointly participated in New Year’s events at Suwa Shrine and prayed together during the Equator Festival for safe voyages. Her situational awareness and information-gathering habits prove vital for the Harekaze crew’s operational readiness.