Miyuki Ayanokōji is one of five wealthy students targeted for assassination at the Seika School for Girls, alongside her older fraternal twin sister Kimiko and friends Youko Ryuuzaki, Reika Shu, and Nina Kirov. She contrasts sharply with Kimiko's aloof and self-centered nature; Miyuki is quick-tempered, particularly reacting to her sister's actions, and exhibits a pragmatic, grounded attitude. She often voices frustration with Kimiko's antics and shows concern for others' safety, objecting to reckless plans and acting as an unintentional voice of reason.

Physically, Miyuki has dark blue hair, grey eyes, stands 1.65 meters tall, and weighs 48 kilograms with measurements of 88-57-87. Her blood type is AB and her birthday is August 31st. Her special talent lies in mechanics, electronics, and computer systems, specifically as a skilled hacker. This expertise allows her to manipulate devices, bypass security systems, and significantly aid the group's investigations and defenses.

When mercenaries attack the school after police protection ends, Miyuki actively works to counter the assailants. She uses her mechanical skills against threats and coordinates survival strategies. During the crisis, she openly criticizes Kimiko's narcissism and dangerous decisions, directly challenging her sister's leadership. However, her rational approaches are frequently undermined by the chaos and Kimiko's interference. Miyuki's background beyond her school enrollment and twin relationship remains unexplored, as the narrative focuses solely on the OVA's assassination plot without detailing her past or future.