This letter was a bit of a foregone conclusion, wasn't it? If you're a regular reader, you know that I'm every bit as comfortable in the dark as I am uncomfortable in the light. I'm pretty obvious that way.
I guess you could say the Dark is like leather. (There's a kink joke in here somewhere...) Ereshkigal's darkness was like my docs and my motorcycle gloves - supportive, yes, but in an eminently practical way. They look cool, but my first pair of docs taught me a lot about patience, about persistence, about the necessity of pain to get what you want, about how breaking in was not breaking down. I still own my first pair of docs. They're still my favorites and my go-to shoes outside of work. The Dark teaches you to keep going even when you can't see the light at the end of the tunnel, even when you can't see the tunnel itself.
Kuan Yin is the soft suede of a blanket or a cloak, keeping you warm and dry, giving you a space to safely fall apart. I fell apart on her often, and I'm not proud of that, but she wraps me up and holds me when I need it. She persists in reminding me that Loving Kindness meditation requires you to practice loving yourself and forgiving yourself as well as your friends and your enemies. The Dark can protect you, if you let go of your fears of the monsters that hide in it. (Remember what Grover taught you - the monster at the end of the book, the thing you are so afraid of? Is you.)
Xuan Nu is a warrior and a fighter, who taught those arts to the legendary Emperor of China. Her darkness is the boiled leather armor that can deflect metal and stone weapons. When I fight for what I want, whether with words or actions, weapons or spells, hers is the Dark I call on. Those monsters may turn on others; the talents that seemed like a liability in my youth can be honed into a sharp, quick tongue, a fierce willingness to fight for the opportunities people need, a sense of fairness that knows it will never be satisfied and pushes ahead anyway. This Dark is not to be trifled with or cast out, because it remembers and it comes for what rightfully belongs to it.
I've spent more time with the Dark than with any of the other aspects, and I've seen others there as well - Angrboda and Lilith, both in the same archetype as Xuan Nu and as Mothers of Monsters, and Loki... Well, his time in the Dark is what turned him into the Breaker of Worlds.
Paths in the Dark are well-hidden but abundant. They're not easy paths to walk - shadows, monsters, coffee tables to trip over. You never really know what's coming, though eventually you get enough of a feel for it to be able to guess. The Dark is internal and private compared to the Light - you're not likely to find a megachurch worshiping the Dark any time soon. For me, that's a plus.
It does make writing about it a little harder, of course. Guess you'll have to look for yourself.
See you underground.