E.T.A.I., standing for Extraterrestrial Artificial Intelligence, serves as the silent bodyguard for Miyu Shiratori throughout AIKa ZERO. She possesses a tall, imposing physique with dark hair and grey eyes, complemented by notably large breasts. Her origins remain obscure, though she shares a clear link with the aliens encountered at St. Aero academy, utilizing identical yellow rope-like tendrils for probing and controlling humans. Miyu Shiratori is suggested as her initial probe target, establishing a unique symbiotic bond where these alien tendrils resided within Miyu's body and obeyed her commands.

E.T.A.I. exhibits significant superhuman strength, demonstrated by overpowering Aika Sumeragi with a single-handed bearhug and later restraining her by the throat. Her role centers on protecting Miyu with minimal dialogue. During the climactic chapel confrontation, she intervenes to shield Miyu from a projectile thrown by Aika, resulting in her being impaled through the torso and mouth by an alien spike formed from the tendrils. This injury leaves her immobilized and unconscious.

After this defeat, E.T.A.I. and Miyu are seen unconscious and naked on separate beds under the observation of Rudolf and Neena Hagen. Later imagery shows their recovery and the development of a friendly rapport with the Hagens. Ultimately, E.T.A.I. becomes the principal of an unspecified academy.