Here's the guide on how to finish the game:
-Go to the guild hall and talk to the purple hair to get quest
-New map storage should appear, go through there and beat the big horned boss
-Go back to guild hall report quest
-"Normal" dungeons portal open, if ready go to the last option in the portal for story progression
-Keep beating boss and going down the level till you reach last level(a box appears when you kill the boss instead of stairs) or get this cut scene of "new" boss appearing
-There should be a portal with heart in the world map, go in it for h-scene
-New option in the normal dungeon at the bottom, go in it and fight the humanoid boss
-Sleep a few days till you get the McDonald girl corrupted scene
-Once you get that, report to guild hall purple hair and go back to storage
-The door in the back that you cant enter before should open now
-Beat the McDonald girl
-Go back to guild hall purple hair and new option available for the demon king castle
-Go and beat boss to get staircase and go up
-There should be portals on ground, use the corresponding portal to go to horn boss and up stairs
-Repeat this for next level till you get to a place with 2 portals
-Going into the next portal will start a boss fight, do this 5x and you be at the last portal
-Go in the portal and fight the boss to finish playthrough
If i missed anything feel free to correct it :3