Miyu Shiratori holds the position of student council president at St. Aero school, commanding the White Knights group. She displays a calm and mysterious demeanor, retaining composure even during investigations into unusual school incidents. Her appearance features long purple hair and a standard school uniform with knee-high socks and a tie.

Approximately one year before the main events, Miyu encountered an alien presence while exploring a cave beneath the school. This led to a symbiotic bond with extraterrestrial entities, manifesting as tendrils extending from her back. These tendrils probe the minds and bodies of other girls, especially those with weak wills, allowing Miyu to control them remotely. The probing harvests energy from victims and may induce memory loss or unconsciousness.

Miyu orders the White Knights to systematically abduct female students, suspending them for energy harvesting. Her motivations for these actions remain unspecified. She demonstrates combat skills superior to other White Knights but shows physical weakness from the strain of her alien-derived powers. Her symbiotic connection includes E.T.A.I., who serves as her bodyguard and is identified as her lover.

Following defeat in a confrontation, Miyu is captured by Neena Hagen and Rudolf Hagen for research on her and the linked alien entity.