User blog comment:Xilinoc/Ch. 669 - 刃 II/@comment-10301320-20160407134643

I don't think those are black markings on his face, in a few panels you can see he has horns, so I think those black markings are just shadows. I think the Bankai is supposed to be based off a red oni type creature.

EDIT: Page 13, bottom left panel is one where you can see the horns and no black markings.