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.
- Vengeful - After being defeated by Juni in the Robo-Arena she is seen actively trying to take him out in the Mega-Race to settle the score. Also, Carmen accuses Demetra of not being real then Demetra returns in kind with accusations of her own.
- Mysterious - We are left wondering how she has a map to the game and how she comes back to life until it's discovered she's a program. It's also a mystery as to whether or not her tagging in for Juni to save him from Arnold was based on gaining his trust to more effectively deceive him or based on care for his well being.
- Intuitive - She defies all her programming by sacrificing herself in the end. This suggest she's acting beyond the purpose she's designed for. Despite being a program meant to betray she demonstrates a clear ability to display other emotions and to act accordingly most notably her apology to Juni for deceiving him, the tears she sheds when they say goodbye, and her holding the door for the others to escape.
- Resentment - Demetra shows a few emotional cues that demonstrate a self-defeating nature: first she displays a sense of profound worry and helplessness while watching Arnold defeating Juni, then when she tags in for Juni to fight Arnold she says "You have to find your sister, Juni!." Her expression was one of urgency and most importantly pain because she went beyond the purpose of her programming in this selfless act. This is also the case in the unbeatable level where her true feeling were again compromised by the purpose given to her, causing immense sorrow.
- "I'm sorry, Juni. But, it's in my programming."
- —Demetra apologising to Juni, Spy Kids 3-D: Game Over
- Demetra could possibly have her name derived from the word "deceiver", which is her role in the game.