What is Dark Essence?
Dark Essence is that darkly ephemeral, completely supernatural thing that propagates your existence long past your human death, carrying you on as an eternal creature of the night. Some speculate it is the source of all Vampiric power, while others refute that it is merely a blood energy that sustains you.
Please Note: This essence is not to be confused with a Soul, which is of course a mystery that you must search out on your own to answer.
How Does it Work?
At the most basic level, the Sphere's properties ensure that it can hold your Dark Essence for one day before your essence loses power and drains away. However, if you return the next day and Focus into it again, you will strengthen it and all within... and it will keep for another day.
The continuous strengthening of your essence by Focusing empowers it to transform the forces of your Unlife into numerous important things.
What Makes this Special?
Glad you asked... *evil grin*
At varying intervals of your Focusing, the Sphere will become ready. When it is, it will telepathically connect with you to offer you a selection of choices on-screen. You can choose from whatever is offered and fly away with whatever you've chosen...
~ or ~
...you may choose to skip the offered choices and continue to strengthen the Sphere with even more Dark Essence. Continuing to Focus will bring you a new and different set of choices at your next interval, and often times will bring an even better selection.
What are the Different Rewards?
During the choice intervals your reward options could be any from the following examples:
Energy and Rage Devourables
Scores of Red Blood and Black Blood
a variety of Powers (including some of the rarest and most wanted in the whole game)
Random Mystery Packs filled with... well, who knows, but it's all good stuff!
New Items, never seen before on the Darkside
...and much more!
So, that's the official line on Dark Essence. In reality you need to go to your sphere every day and click to focus, as it says above, and at various intervals it will offer a reward, or you can skip in the hope of a different reward next interval.
You can only focus once every 24 hours, then you have a full 24 hour period in which to focus again. Don't miss a day or it will reset and you'll have to start over! ;)