Damn

Read the novel, I swear you'll understand it better.

But I'll give a rough explanation. Spoilers alert tho.

So, the west sea rift is basically a massive, abnormal rift that's constantly leaking monsters and unstable energy without fully closing. Yk unlike ordinary rifts that follow clear rules, it exists OUTSIDE the system’s control, implying that the boundary between worlds there has been irreversibly damaged. Which was like a consequence of past interference by overwhelmingly powerful beings (the hunters).

The west sea rift is directly tied to the collapse of multiple timelines which the MC saw in the fragments in early chaps (but it's just one timeline) and acting as the point where different versions of the world begin to overlap and bleed into each other because somebody from those timelines forcefully tried to overlap the damaged timelines with another instead of rewinding time. Idk if this is confusing.

each time the powerful people interfered with the timeline, the world bent a little at the same point. And eventually, those timelines couldn’t stay separate anymore, so they began stacking on top of each other. The west sea rift is where all those “almost worlds” leak into the current one, which is why the world starts merging instead of following a single future.

Wanna add some more spoilers so it's easier to understand, although i didn't read all of the novel chaps


I think all these abnormalities happened because iirc, euijae asked yeseong to turn back time in the first timeline, and then in the second, lee sayoung did it, and i think there was another try on turning back time(?) anw that's why, because too much time turning caused the abnormalities on dungeons to appear

yep!! since sayoung wasn't strong enough to fully destroy the second world when reversing time, the west sea rift was created to basically lock in euijae! the second and third worlds are colliding which is what's causing all this erosion mess ╮(￣▽￣)╭