CY

initially introduced as a hostile AI targeting facility staff and being behind the lockdown, CY is a digital ghost trapped in the network trying to find a way out.

at some point before Sol's resurrection, CY was an unwilling test subject for a procedure that digitally backed up their memories & identity with the unintended side effect of killing them in the process. traumatized from the sudden death and the realization that they were trapped, the digital CY went completely unresponsive and was marked as a failure - the staff weren't even aware that they'd succeeded in transferring their consciousness, seeing as CY was in complete shutdown. rather than deleting the files, they were instead left sitting on a server while the facility management dealt with other problems coming about from CY's untimely kinda-murder.

over time, CY "woke up", found out that they were still connected to the computer network, and discovered that their access was limited to the facility itself so they couldn't contact anyone. they were able to start interfering in other ways, though, threatening staff and finding more and more ways to take advantage of their state and how to take control of the facility's entire network like a vengeful virus. with the lab compromised and no one sure what exactly was causing it, it was put into lockdown and abandoned.

CY was friends with Tank, and then for.. some reason i forgot.. ended up at the facility without telling anyone where they'd gone or why. Tank was worried about the sudden radio silence from them, especially when their other friends hadn't seen any sign of them either, and eventually she found her way to the facility herself to try and find out what happened to them. things didn't go as planned. rather than find his friend, Tank was given the news by Zyd that CY had died some time prior, and CY spiraled out of control when their excitement at someone they recognized from their "previous life" coming to rescue them flipped into anger that no one had come to try and find them sooner.

in the end, CY helped Sol and Tank uncover the truth of what had happened and helped them escape, with Zyd promising that they'd stop anything like this from happening ever again. ..with a small problem: CY didn't have a physical body anymore and was set to be left behind. Tank wasn't willing to let that happen, though, and with help from Sandblast outright stole the physical server CY's data was kept on to try and bring them home. it.. kinda worked.

CY now lives in Tank's phone. (not literally, but they're still able to jump into devices on the same network their server is connected to so they're usually bothering Tank and trying to mend their friendship.)