Miyabi Koigasaki is a 17-year-old female from Kochi Prefecture, Japan, born on July 27, 1998. She stands 160 centimeters tall with black neck-length hair featuring blunt bangs and striking red eyes. Her typical attire includes detached sleeves, a hair ornament, and stockings.

She possesses world-famous hacker-level expertise in computer skills like hacking, programming, and cracking. To support her duties, she personally acquired a supercomputer from the Information Management Bureau. Her speech blends internet slang, IT terminology, and the Tosa dialect of her Kochi upbringing. She also demonstrates skill in preparing Japanese-style meals.

Within the Trinary task force—which addresses artificially created reality-overwriting pocket dimensions known as Phenomenon—Miyabi provides rear support during operations. Her responsibilities encompass aerial functions, analytical assessments, and technical assistance. Purple is her designated personal color in this role. She refers to her specialized equipment as her "partner," indicating a close operational bond. Her analysis helps resolve Phenomenon events, including those generated by teammate Tsubame Ouse.

Miyabi maintains a long-standing online connection with an entity called Mayu the Rabbit Anima. Outside tactical duties, she volunteers in Phenomenon-affected areas, earning her the real-world descriptor "angel" due to benevolent actions. Personality observations note an expressionless demeanor coupled with a motherly disposition toward teammates, despite being the second-oldest member. She balances everyday life with managing reality-threatening incidents as a tech-focused individual.