Tsugumi Yagi, affectionately known as Tsugu-chan, is the Harekaze's telegraph operator and communications specialist. Her family runs Yokosuka's Suwa Shrine, where she serves as a shrine maiden; this location holds significance for others, notably as the place where strong winds swept away Mashiro Munetani's mother's captain hat. Tsugumi possesses unique dowsing abilities discovered in childhood, locating an oil field on her elementary school playground and later a hot spring behind her middle school, contributing to her reputation for unusual luck. She holds certifications as a Third-Class Maritime Radio Operator and a Weather Forecaster. Her smartphone typing proficiency allows her to efficiently record ship communications, replacing handwritten logs. Curious and energetic with a unique worldview, she often surprises others with unconventional ideas while maintaining a cheerful demeanor. Physics is her strongest academic subject, while social studies poses challenges. She frequently reads e-books to gather knowledge and cautions that incorrect knowledge is more dangerous than ignorance. Beyond communications, she collaborates closely with Megumi Uda on ship duties and recognizes others in shrine work, such as recruiting Rin Shiretoko to assist during New Year events at Suwa Shrine. She also participates in ceremonial activities like prayers for voyage safety during the Equator Festival. She favors the color yellow and sweet foods like sweet rice drink (amazake) and sugar candy (konpeito), but dislikes konjac. Her birthday is January 28th, making her an Aquarius. Her mother works as a barber. Tsugumi chose to attend Yokosuka Girls' Marine High School because her dowsing indicated this path.