This is an interesting and complex attempt to fuse theology and myth (of course, that's a difference without a distinction from most POVs), to create a unique backdrop for this Snarry. Again and again, I found myself wanting to debate the alternate reality of this Beneathworld with you, which is a tribute to how much it engaged me.
Snape and his mother are well-realized here. Indeed, that is almost a give-away, for me. Because if you're who I think you are: no one writes Eileen the way you do.
Anyway, whoever you are: thank you. I enjoyed reading this late at night, during a week when I was very stressed with work. This served wonderfully well, as escape literature for me.