User blog comment:Xilinoc/Ch. 580 - THE LIGHT/@comment-4957813-20140514212807

I'd say it's Ichigo. the skull is Ichigo's main symbol, plus the entrance of this new combatant is made in the context of Kenpachi's fight. And aside from Ikkaku, Yumichika, and Yachiru, no one is more associated with Kenpachi besides are wayward protagonist.