It only says “in the darkest night, trust meager light” and idk how to finish the quest
You aren't supposed to fight the dark orb, its kinda just there for show. The game is bugged and normally Asmodea is supposed to give you a hint but you have to go up from the entrance and into the looping 4-way intersection. When you arrive there, take the doorways in the order Right, Up, Left, Left, Down, Right, Up, Down (I think. let me know if it doesn't work). You should find a tarot and then brought to a boss room when you leave. This part is super confusing and I didn't even figure it out on my blind playthrough.