My theroy is that MC is one of the programs, like the black cat. Xian would be the hero that he followed around. The cat system said they used to have human systems, but that they no longer make them like that due to unknown reasons. Would explain his bright green eyes. Also, one of the panels from 105 had a gradient on his eyes, of a more yellow green to green, with a kinda red corruption look on it.
Maybe X fell for the human system, and he wanted to be with him so badly he broke MC? Not sure, but that is my theroy.
that's what i understood too. ML was the transmigrator and MC his system, ML finished all the missions splendidly and obtained mindreading at some point and their relationship took a turn (probably found out MC loved him too thru it?), but systems and transmigrators cannot be with each other, so ML used his power etc. so he could be with MC, which seems so far meant that he "broke" MC so he isn't a system any longer. MC being a former system also would explain his lack of empathy and human emotions etc.
i hope the official translation will make it clearer because i don't think the manhua is subtle about it haha

Oh shit
I just noticed that in order to change worlds he needs to die right? I mean that's what I understood. (please correct me if I'm wrong) that means, that in the first world, in order for him to leave, he had to die??? Or did he just transport???
If anyone understands more than me please tell me, I'm utterly confused