Webtoon
Worth the Candle

3
Juniper: His name is Juniper short Joon. Juniper was always the Dungeon Master, never the player. He was always a creator of worlds rather thsn the one who walked within them...until now. Somehow, the tables have turned in the most dramatic way possible. Juniper finds himself in a world filled with the wildest fantasies a mind could come up with, and his fingerprints are all over it. Throughout this world, echoes of his own ideas and plots leave him feeling like he's always one step behind. He finds bits and pieces of ancient influence strewn about every town he goes through. One thing is clear, though: Juniper walks this magical new world in someone else's shadow. It might all add up to something vital...if only he can survive long enough to figure it out.
You: you can choose everything about you, but you're not from that world too. You're from the real world like him, you were his old classmate.
(Credit to the creators: Alexander Wales, Betofu) (I found it on Webtoon I did read the first three episodes the name is Worth the Candle)