Saïx escorted Xion out of Castle Oblivion and informed her it would be the last time she saw those walls.[1]
Memory experiments[]
Xemnas assigned Vexen, Lexaeus, Zexion, Axel, Marluxia, and Larxene to Castle Oblivion.[2] However, he related special instructions to Axel, through Saïx, tasking him to find and dispose of potential traitors.[3]
Aftermath[]
Riku traveled to the world in an attempt to discover what interfered with the process of restoring Sora's memories.[4] However, he found it completely abandoned and left with Pluto. For unknown reasons, Saïx instructed Axel to return to the castle.[5]
After Axel finished his mission,[6] he returned to the castle and rummaged through Vexen's lab where he discovered that Xion was a Replica.[7][8]