Mutsuki Sakaki is a member of the development team of Under Anchor Tech, the technical branch of the organization responsible for the maintenance and upkeep of the Phone Bravers and related equipment. Her precise duties within the team are not extensively detailed, but she works alongside fellow technical staff such as Mayuko Hasekura, Sayaka Kisaragi, Yayoi Kageyama, and Hirofumi Morishita. Notably, she appears to have taken an interest in Hirofumi, suggesting a potential personal or professional connection between them. No further background, personality traits, motivations, or specific story contributions are documented, and she does not undergo significant development over the course of the series. She has no known combat or special abilities.