Code Lyoko

Four ordinary junior high schoolchildren, Jeremie, Odd, Ulrich and Yumi, must help a virtual humanoid named Aelita to stop the evil computer program Xana from attacking Earth by traveling to Aelita's home, and virtual world, Lyoko. Jeremie does not travel to Lyoko, but instead tries to find a way to bring Aelita to Earth. After accomplishing this goal, they must continue fighting Xana, while trying to figure out Aelita's connection to Xana and her past life as a human. Source: Wikipedia, "Code Lyoko (video game)", available under the CC-BY-SA License.