ok. ok i've rewatched all 8 episodes and rambled at multiple victims. here's my final theory before the last episodes are released.

everyone's confused about how there doesn't seem to be enough time to introduce the time travel plot but also that they seem to have already included time travel elements. solution:

the events we see in the drama outside of the fire flashbacks is the regular, unchanged timeline. that really is the story of how jin met the others and became friends with them, and also how their personal tragedies unfold. if this was a linear narrative then the next episodes would be about how it all falls apart like it did in the original storyline. realistically it would leave it at an open ending right before the time loop events of the webtoon. if they did somehow include the time loop, it would have shown jin's attempts at trying to save his friends and so on.

but! it's not a linear narrative - time travel's already involved. it was basically confirmed with the two jimin pov scenes where he tries to warn the police about the fire. in the first one he stumbles and is too late, and in the second one he's given a script and is successful. so there's someone time travelling and changing the decisions that were made this day. that person texted yoongi not to leave his mother, directed tae to stall yoongi, and was the one who handed jimin the warning.

it's jin. most likely, it's jin. we haven't gotten his pov of the night yet, and we have that one scene of the capped figure flicking the lighter that belonged to jin's dad. not only does it follow jin's role in the original storyline but it's also being narratively set up by the show itself by how it keeps putting up parallels between jin and his dad. reminder that jin's dad also went through the cursed time loop in an attempt to save his friends and made the same sacrifice of losing his memories, exactly like jin did in the webtoon.

so what's with current jin? basically. the flashbacks aren't actually flashbacks. the original timeline unfolds and then at some point in the future jin decides he has to use time travel to fix things - the events in those flashbacks are the things he changes. the unknown number and capped figure is jin from the future episodes travelling back to a time where his younger self was still in america to try and save his friends without having to interact with himself because it was before any of the others would meet him two years later. Or if we're sticking with only one body then its just young jin with old jin's memories.

they are running the high school segment and the time loop plot simultaneously. maybe in the original event the others weren't even involved in the night of the fire. maybe having all of them be involved means that they avoid something tragic thats about to happen, or causes a chain reaction to happier circumstances.

... i'm trying ok. my only other guess is that the principal is the one time travelling to try and kill yoongi/cein in the fire so he doesn't out him. so.