It is second part of Anya's event, like you were told before.
By the way, have you tried 90/12 map or you just watched some video and thought "It's too difficult for me"? The map itself may look scary, but it's quite easy if you try it. I've managed to get 3* with just cc40 Bashira, aw41 Spica, cc55 Pallis, cc35 Odette, 2 healers and 1 soldier. And reward is ~19-24 crystals per run.