Note: Arias may be female due to this line:
"Why can I just hear this woman smirking when she wrote that?"
My understanding of the backstory of the labyrinth:
Arias, a lesser demon who's a butler and bodyguard to The Lady Of The Labyrinth writes in her diary.
From there, we learn about her family. Ariane, and Arianna (who are the maids), the youngest sibling who get's skipped over (she never did take over the diary), and Archfiend who's a spirit that's bound to armour by the Lady.
The labyrinth is in the form of a castle (which may have once been a real place). There, traps are set in place to ward off intruders. Mostly adventurers who thought the castle had hidden treasure (that's false).
There was, however. A particular individual of note is the Knight. She's powerful and deals with the traps rather easily. The Lady and the Knight fight/spar every Thursday.
One day, the Knight didn't appear. Instead, members of Umbra invade the castle so that it can be used for void-related purposes.
The traps were unsuccessful due to Umbra members going into the labyrinth from the upper section. Arias, the twins, and the Lady herself died.
Archfiend is the only one who's spared. The labyrinth that is the castle becomes an illusion, and the Archfiend becomes a shade. He resurrects the twins as lesser shades, and is now hellbent on resurrecting the Lady by sacrificing people to the void.
...I wonder what will happen to the Archfiend when Akemi consumes/absorbs him though?
Edit: I don't know what to make of this. But it might be related to the youngest sister.
The smell of smoke hits your nose. The room in front of you is engulfed in flames. The gray walls and glass mirrors are torn and shattered. Beautiful paintings, and sturdy wood all burn down and fall to the ground around you.
Nothing in this room is sacred. There is no magic here, no god here, no good here. If a room is filled with emotion in the best of times, this is an empty box. You take one step in, sword almost unconsciously raised up.
You regret it instantly. There are screams. A deafening scream cuts through the air, along with a simply ear splitting laugh, like a mockery of the villains of the children's shows you will always be too old and too tired to watch. There is a striped horn on the floor. It has been broken off from someone, or something.
And somehow, you hear a woman's voice in your ear. And what she says chills whatever was left in your heart into ice.
"Murderers. Murderers, all of you. You're just someone who fights for money, not any of the good things in this world! You're no better than your bloody swords and your empty churches."
"I'll see you soon in hell."