With the March 10th patch, we can now enchant our accessories, using something called Magical Essence as payment... yet the developers failed to update the Help information on where to obtain Magical Essence!

You obtain Magical Essence from feeding unneeded accessories to your Black Spirit... the same way you get Magical Residue from feeding him unwanted gear. Also just like Residue, the accessories need to be purple (or better) to receive any Essence.

In order to obtain Magical Essence you need to feed your spirit with accesories