Gemini is stringent in his reform school duties and unwaveringly loyal to Miss Heinous. He appears to be just as fixated on orderliness as Heinous, as he orders newly arriving princesses at St. Olga's to "respect the queue". Because of his loyalty to Miss Heinous, Gemini bears some jealousy toward Rasticore, to whom Heinous displays much more affection.
Gemini also appears to be infatuated with "Princess Marco", owning a doll of her and calling her "the fairest in the land".
Gemini is a short troll-like robotic man with wrinkly purple skin, a hunched back, and a large underbite. His head is covered in thin hairs, liver spots, and stitches. He wears an all-black uniform and a strange eyepiece with an orange or yellow gemstone that functions as his one eye. His left leg is a metal prosthetic.
In "St. Olga's Reform School for Wayward Princesses", Gemini serves as Miss Heinous' assistant and works alongside her to maintain the school and reform its students into perfect princesses. He welcomes new arrivals to the facility and also voices over the school's infomercial. Despite his and Miss Heinous' efforts, however, Star Butterfly and Marco Diaz infiltrate the school and instigate a princess rebellion, leading Gemini and Miss Heinous to lose their jobs.
In "Gift of the Card", Gemini is living with Miss Heinous in a rundown apartment complex with very little money. Despite his complaints of hunger, however, Heinous sends him on an errand to buy hairspray with the last of their money.
In "Heinous", Gemini accompanies Miss Heinous and Rasticore's regenerating arm to Earth to demand justice from "Princess Marco's" parents. During the visit to Earth, Star attacks him with a Narwhal Blast. After some time spent negotiating, he and Heinous punish Marco by filming a video addressed from Marco to the princesses he inspired, in which he renounces the words he used to incite the revolt. That night, Gemini goes to sleep (in the trunk of Miss Heinous' car) with a Princess Marco doll, having apparently also been moved by her rebel nature.
In "Princess Turdina", Gemini tries to help Miss Heinous retake control of St. Olga's school, but they get chased off again. He also calls attention to the fact that Miss Heinous swears revenge on Marco very often.
In "Monster Bash", he assists Miss Heinous in capturing Marco in an attempt to drain his youth. He becomes unnerved when Miss Heinous is drawn towards a hidden room in the monster temple, and starts to recall memories associated with it. When Mina Loveberry challenges Miss Heinous's identity, he angrily defends her reputation, and he is shocked when her true identity (Meteora Butterfly) is revealed. He still remains loyal to Meteora despite this revelation, fleeing with her and Rasticore at the end of the episode.
In "Skooled!", Gemini helps Miss Heinous invade St. Olga's school again. At the end of the episode, he is revealed to be an android like the rest of the school's guards, and Miss Heinous rips out his heart out of anger over Rasticore abandoning her, causing Gemini to shut down.
- Theme Song (season 2 & 3)
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- Gemini's name is a double entendre, referring to both the constellation and as a pun about his single eye ("gem in eye").