Hear me out about who player worked as.
I been obsessing over Poppy Playtime and I always thought about that specific line in 'Story so far' (Chapter 1). The line says that Harley is kinda impressed how easily we navigate vents. So what if we worked in moving crew actually? We moved experiments between locations so we should know various catwalks to cut distance. And the fact that player has very specific nightmare about Huggy Wuggy. Welp remember that tape when huggy escaped? Probably we was a part of moving crew back then so that's what caused trauma. Another thing, the player is guilty about something or someone. Maybe when the hour of joy was starting and moving crew was moving kissy missy, then it was probably our shift but we maybe switched with our friend and our friend took the bullet for us. Another thing that in CatNap's nightmare sequence there is radio host saying this: "I find your presence intrusive. After all this time you return. You come in here and you kill and murder; you pillage and destroy! Your presence was demanded 10 years ago and you didn't show up. 8/8/1995. You were supposed to be here. Why weren't you here? You missed the event, you missed the meeting, you missed the party! YOU HAVE NO RIGHT TO BE HERE. 8/8/1995.". Your presence was demanded 10 years ago, so maybe it was player's mind saying that they should have died instead of friend. But I am still a little bit confused about killing and murdering stuff. Yeah it's probably our hazed mind saying that. So that's my theory. It's small one I had in my head. My theories often suck though, but it's first one which I thoroughly thought (Even if it can be incorrect).