Code Lyoko and Digimon 02.
While travelling back from a replica the Skid gets attacked, during the attack Odd is separated from the rest of the group. With his power failing Odd makes his way to what he thinks is an open replica. But it's actually the 02 version of the Digital world, XANA had found an entrance to it and had sent some of his monsters through.
Meanwhile the Digi-destined are busy looking for a new Digiegg signal when they run into XANA's monsters, their Digimon struggle until Odd shows up and helps fight off XANA, XANA retreats but seals the connection between the Digital sea and the Digital world; leaving Odd trapped in the Digital world.
The Digi-destined take Odd back to their world, which is in another dimension to Odd's Earth. The next day the Digi-destined and the Lyoko warrior head back into the Digital world to find the Digiegg. The Digiegg belongs to Odd; Odd is the child of Destiny and is partnered with a cat based Digimon.