Nagatsuki Kuron hails from China and becomes pivotal during the second season’s events, declaring Mutsuki Ichimonji her true mother figure. This bond originates from a childhood park encounter where Mutsuki, then a high schooler, mistook her for a boy and formed a protective connection that fostered Nagatsuki’s enduring respect and affection. Physically, she possesses black hair, brown eyes, and stands 1.65 meters tall, preferring masculine attire due to discomfort with feminine clothing like short skirts—though she occasionally wears a red dress, notably during her introduction.

Her personality merges combativeness with fierce loyalty. A skilled Kung Fu practitioner, she frequently clashes with Chitose Hitotose as they compete for Mutsuki’s approval, cementing their rivalry. Beneath this confrontational exterior, she shares Chitose’s traits: emotional reserve, diligence, and deep reverence for cherished figures like Mutsuki, whom she endearingly calls "a lotin" (a Chinese-derived term). This complexity aligns her with the "Jerk with a Heart of Gold" archetype.

Nagatsuki’s arc revolves around integration and shifting dynamics. Initially rivaling Chitose for Mutsuki’s maternal affection, her status intensifies upon becoming their neighbor. Her interactions with Chitose evolve from hostility to contentious coexistence, culminating in her confessing romantic feelings for him. She ultimately embraces her place within Chitose’s unconventional family, broadening her focus beyond Mutsuki. An avid fan of pop idol Hazuki Yazakura, this fandom adds relatable enthusiasm to her intense persona.