I have no clue what happened in the netflix remake but the ending to the webtoon was
*SPOILER*
Hyun and Hyuk both turned into monsters, Hyun turning into a knight of some sorts to try and save the others before fully losing consciousness, Hyuk turning into a massive glob to try and stop Hyun from hurting the others.
Hyun ended up turning into this weird monster/human (i honestly still don't understand what it is) where he's just naked, and can't feel anything. He finds his old phone with the song that Jisu played and he started crying. (I have no clue what happened to Hyuk)
The others are in a military base (I think?) and one of them spots Hyun in the middle of the snow. They all rush to hug him and thats it.

This emotionally destroyed me, i was so emotionally attached to Hyun and Hyuk, seeing them sacrifice themselves to save the others just made me bawl my eyes out.