Natsuki serves as a supporting character in the series, working as a nurse at an isolated hospital. She possesses blue hair and light skin. During daylight hours, she carries out standard nursing responsibilities alongside her colleagues, tending to elderly patients. After nightfall, when eerie music echoes through the hospital’s speakers, Natsuki and the other staff succumb to overpowering sexual urges, resulting in uncontrollable actions. She participates in the core mystery surrounding the music’s source and impact, though her personal methods or inquiries remain unspecified. As the series progresses, her role diminishes with fewer lines and less active involvement in events. Her background, development, and life beyond the hospital remain undocumented. Relationships with fellow nurses Mikuru, Saeko, Haruka, and Eri exist within the group dynamic but lack individual depth. Her motivations extend no further than the music’s influence.