Ok, not sure where you're up to, but spoilers until chapter 173:
Y did become human and reincarnate as Wang Yi (he died as a system). Wang Yi lives a normal human life, then the bus accident happens, where his male friend almost dies and becomes comatose (I think Wang Yi tinks he died) and many other die. Wang Yi mistakenly believes the accident is his fault, which is when So appears and recruit him as a villainous host. Bai mo (his female friend) also becomes a host with the same goal of changing this event thanks to an expensive item in the system shop.
Now for the theory part: for now it's unclear if the systems had anything to do with the accident or if the world Wang Yi was in was truly our normal human world or a novel world and the accident was part of the plot.
What happens to his friends then? Were they just memories.. but mc meet one of his friend (the girl) who was she then I'm confused