The sixth season begins a time after the fifth season, where X.A.N.A. resurrects, and there are new characters: a new professor of Latin named Evan O'Donnell and a student named Alex Nicolas. Alex joins the team being the new Lyoko-Warrior. There are new X.A.N.A. monsters (the mini-Kolossus), a new sector (the Cosmic Space) and William returns that is reincorporated at the team and goes back to Lyoko. Sissi also does it and there are eight Lyoko-Warriors in this season. It's revealed that Ulrich has a twin brother (Eldrich), the virtualized people also can forget things with a program added by Jeremy at the return to the past, and that the sector 5 has a place where X.A.N.A. saves to the monsters defeated called "Purgatory". More advance in the season, there are another time travel where Ulrich goes 7 months to the future where X.A.N.A. has taken the control of the country with some robots called "sentinels", Mrs. Hertz becomes the director with a dark side, Mr. Delmas and Jim are sacked and other changes. The season concludes with the kidnapping of Yumi in the abandoned complex by the spectres of Takeo and Akiko Ishiyama leaving an uncertain state.