Code Lyoko Season 2 Episode 12

After Xana possesses the principal of the school and kidnaps Odd and Yumi, he gives Jeremie an ultimatum: deliver Aelita to the Scyphozoa or sacrifice Odd and Yumi. However, Jeremie and Aelita go to Sissi for help and Sissi agrees to be tempoarily part of the group to help save her father and eradicate Xana.