Sister Grey operates from the extraterrestrial spacecraft Cthulhu's Moon as a close associate of Iczer-1. She engineered the Iczer line of artificial combatants, including Iczer-3, to confront threats. After Iczer-1 sustained injuries battling Neos Gold, Sister Grey oversaw her recovery. With Iczer-1 incapacitated and Earth under imminent invasion by Neos Gold's forces, Sister Grey calculated the urgent need for intervention. She strategically deployed the still-maturing Iczer-3 as Earth's defender, acknowledging the gynoid's incomplete state but prioritizing planetary defense. This decisive action initiated Iczer-3's mission alongside Nagisa Kasumi, granddaughter of Iczer-1's original partner.

Physically characterized by green hair and aubergine eyes, Sister Grey's responsibilities encompass overseeing the deployment of the Iczer units and advising on interplanetary defense strategies. Her recommendation for Iczer-3's early activation stemmed directly from the critical threat assessment during the conflict against Neos Gold.