For any new players, revival crystals will be distributed in the 2nd phase of the White Emperor's event. Both Karmas and Miruno will be available in TP for revival crystals. I would definitely recommend focusing on Miruno since she is a powerhouse of an angel and gives all angels status immunity as her AW passive. Plus, she has a whopping 400 ranged skill upon skill activation with block 1 so she can reach places where other ranged units cannot.
Here are her stats for anyone curious: http://aigis.wikia.com/wiki/Miruno
I'll definitely be getting black Karma with the RCs I've been stocking up from the previous revivals. After Anya, she's gonna be my second princess.