Demetra is the hidden secondary antagonist in Spy Kids 3: Game Over. She is Juni's love interest. She is played by Courtney Jines.
Demetra was first seen at the Robo-Arena, where she and Juni faced off on giant mechas. Demetra won the first round, and Juni won the other two, costing her seven lives. She appeared again at the Mega Race, with her face covered by a helmet. Her vehicle was a high-tech unicycle. During the race, Juni threw a pie from his vehicle, temporarily stunning her. Demetra got a construction-based vehicle with a magnet. She managed to magnetize Juni's motercycle, but he still won on a hubcap. After his victory, Demetra joined him and his friends on their quest to Level 5. On Level 3 and fearing that Juni would lose, Demetra sacrificed herself as one player has to lose against another.
Demetra reappeared at Level 5, claiming there was a glitch in the game and have found an exit. She was then exposed by Carmen as a computerized human being created by The Toymaker in the role of the Deceiver. As the kids were escaped the game, Demetra closed the gate to prevent the levels' guardians from reaching them.
- "Sorry, Juni, but, it's in my programming."