Mutsuki represents the historical Imperial Japanese Navy destroyer, the first in her class to carry large 61cm torpedoes. She possesses a consistently cheerful and energetic personality, often showing responsibility and offering support to others. Her speech features distinctive quirks, ending sentences with "nya" or using playful interjections like "oyo". She quickly befriends Fubuki upon Fubuki's arrival at the naval base, acting as one of her first guides and companions. Serving in the Third Torpedo Squadron, she participates in numerous sorties and operations. Her bond with her sister ship Kisaragi is especially significant; Kisaragi exhibits a more mature demeanor despite being younger. During Operation FS, Mutsuki transfers to the Fourth Fleet alongside Mogami. A pivotal moment occurs during the Battle of W Island with the sinking of Kisaragi, an event that profoundly impacts Mutsuki, though she continues her duties. The film adaptation depicts Kisaragi later resurfacing with amnesia and post-traumatic stress, recognizing only Mutsuki. Kisaragi gradually transforms into an Abyssal vessel while holding fragmented memories, yet Mutsuki remains devoted to her sister throughout this ordeal. In the climactic mission to confront the source of Abyssal power within the Crimson Sea, Mutsuki accompanies Fubuki and Yamato. After sustaining heavy damage, she witnesses the partially transformed Kisaragi provide crucial assistance. Following the dispersal of the Abyssal threat, Kisaragi vanishes after exchanging final words with Mutsuki. A post-credits scene implies their eventual reunion. Her combat capabilities progress through remodels, achieving her Kai Ni form at level 65. This upgrade increases her torpedo stat to 79, evasion to 90, and anti-submarine warfare to 69. Her standard equipment includes a 12.7cm Twin High-angle Gun Mount, an oxygen torpedo mount, and an enhanced boiler. She also demonstrates compatibility with specific equipment combinations, such as increased firepower and accuracy when pairing certain guns with radar systems. Seasonal dialogue lines reflect her participation in naval base festivities, like offering chocolate during Valentine's Day events. Her quotes consistently express admiration for others and dedication to her duties, with MVP lines emphasizing her desire for recognition and praise.