Mutsu appears as a petite girl with a black bobcut, yellow eyes, fox ears, and a fox tail. She wears a white sleeveless miko shirt with red accents and a matching short skirt secured by a silver belt featuring a yellow circular buckle. Her outfit is completed by black thigh-high socks, red flats, white detached miko sleeves with red trimmings, red strings wrapped around her upper arms, a colorful hair ornament, and a red hagoromo. An alternate "Warring States Warship" skin outfits her with a helmet and swords inspired by a Japanese warlord. She possesses a cheerful, childlike personality marked by high energy and deep curiosity. Mutsu constantly asks questions about the world, from simple natural phenomena like why the sky is blue to complex subjects like the causes of conflict and social customs such as Valentine's chocolate traditions. Despite her playful demeanor, she shows fierce determination to protect her friends in battle. Within Azur Lane, Mutsu is a Sakura Empire battleship. She is identified as the second ship of the Nagato-class and Nagato's younger sister. She references her historical role as a former flagship of the Combined Fleet alongside Nagato, later succeeded by Yamato. Voice lines occasionally allude to her real-world sinking due to an unexplained magazine explosion, mentioning concerns about her "third turret." Mutsu attends the Vanguard Academy as a student. She enthusiastically participates in leisure activities with other shipgirls, such as visiting amusement parks like Manjuu Land alongside Nagato, Yukikaze, and the destroyer quartet. In combat, she utilizes the skill "Big Seven: Sakura," which provides a 20% chance (40% when maxed) to fire a special frontal barrage upon using her main guns, with damage scaling based on skill level. Her gear slots accommodate battleship main guns, destroyer or light cruiser secondary guns, and anti-aircraft guns. She maintains a close bond with Nagato, often seeking to include her in activities. Mutsu interacts with others like Urakaze, who crafted her Warring States equipment, and Mikasa, with whom she discusses desserts. Her dialogue reflects a developing emotional connection to her commander, evolving from general curiosity to expressions of affection and a desire to understand romantic feelings.