X was one of the many Worker Drones that were tested on by JCJensen in terms of how the Absolute Solver worked. It never affected her, and she was cast to the side with others that didn't get the virus. When the core collapses, the Sentinels that normally kept the test Drones where they were meant to be malfunctioned and killed every Drone they came across. She met Alice, (the Drone we see at the end of episode 6, Dead End) and they kept each other alive for almost a week. When Alice disappears, X tries to find the exit herself, assuming Alice died but ends up getting attacked by three Sentinels. She barely manages to escape, but she is wounded beyond repair. She can't remember anything, not even her own name. She's found by K a few days later, when her systems are on the verge of shutting down. K, despite the fact he would usually kill any Worker he meets, feels bad for her. He says he can save her using the parts of the dead Disassembly Drones nearby. Too weak to understand, she agrees and wakes up as X, the personalities of both who she used to be and the Drone who's body she's in now intermixing with each other.