Responses

Given that the destroy world in the dungeon had people similar to the real world proved by the fang we might have a situation of multiple timelines with one of the timelines being the dungeon world, one being the world shown by the s class high school girl and the current timeline. Mainly I think they are separate timelines because J didn't think he was back in the dungeon when the high school girl showed her the fragments. She most have the power to see the destroyed worlds.
I feel like J went through the destroyed world the psychic showed and that is where he got the fang. I also feel like the ML is the one from that world but maybe doesn't remember? He is too obsessed with J or maybe it is just because J saved him