User blog comment:Xilinoc/Chapter 530 - Dark of the Moon 3/@comment-1268838-20130313175949

I'm on the fence about whether it is an imperfect Arrancar or a Vasto Lorde, though I suppose both are possible. I am more leaning towards the latter since it seems to fit the profile Hitsugaya described (human-sized, apparent captain-level power). Assuming this is the thing that is going to floor Isshin, of course. Though, Aizen has expressed interest in both over the course of the series, so it could go either way.