So recently I got stuck, but I figured out a way through this part of the dungeon.
Guide to Find the Key in the Central Line
All credit goes to Monsterdagger!
Go Back to the Start of the Area
Go back to the start of the dungeon and talk to a demon behind and to the right of the main entrance after getting past the first miniboss (the one with the old man).
Wait around for a demon to spawn here (Not the enemy demon in this screenshot).
This dialogue should play.
It’s worth noting that you have to talk the old man first, and then find the demon with the key.
This was when I knew the game was mid
I’m used to bad design like this but I’m genuinely concerned that other people are going to need help figuring this out – especially since this is how the game handles most of its fetch quests
Good on you for making this guide though.