Demetra is the secondary antagonist in Spy Kids 3: Game Over, whom Juni had a crush on.
Spy Kids 3-D: Game Over
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 six 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 the victory, Demetra befriended Juni and joined him and the other gamers on their quest to Level 5. On the way to level 3, Demetra met up in secret with Juni to share two secrets: she knew that Juni wasn't "The Guy" and that she has an illegal map of the game. However, two of the Toymaker's henchmen caught them with the map and threatened them, only for Juni's grandfather to intervene. When Juni bumped into a rare life-pack, a power-up that filled the life counter back up to 9, he decided to give it to Demetra as he owed her it from the Robo-Arena and that he wouldn't want anything to happen to her. Demetra thanked Juni for this. When Juni and Arnold faced each other in the battle to get to level 4. Demetra couldn't bear to see Juni losing against Arnold, so she sacrificed herself for Juni so that he could save his sister. Arnold defeated Demetra in one hit and she got an immediate "game over". Juni was heartbroken and he never got her e-mail address.
When the gamers finally got to level 5 later on, Demetra reappeared much to Juni's delight. She claimed there was a glitch in the game and managed to get back in and then said she found an exit for everyone. When Carmen asked Demetra who she was, she said she was Juni's girlfriend and that she had been helping him to win the game. Carmen didn't believe her and explained to the gamers and Juni that she was the deceiver, a programme used to fool gamers. Demetra tried to convince to Juni that Carmen was lying and that she could have been brainwashed, but she was finally exposed as Carmen swung for Demetra's head only for her arm to go straight through, proving she was also computerized. Juni was once again devastated, and a guilty Demetra apologised. The Toymaker then appeared and set a giant robot onto the gamers. Juni's grandfather then showed the real way to the exit, and everybody quickly ran towards it. Demetra shed a tear, and sacrificed herself to save the other gamers from harm by closing the gate to the exit. What happened to Demetra was unknown, as that was the last time she was seen.
- Demetra could possibly have her name as it sounds similar to "deceiver", her role in the game.