User blog comment:Xilinoc/Ch. 577 - SWORD/@comment-4207271-20140416082233/@comment-11051098-20140416161122

My thoughts is that the jagged, worn sword is actually his sealed Zanpakutô, since the giant ax-thing appears to be the real Shikai.

And I agree with Xilinoc - it appears to be just a huge physical ax-thingy with no special abilities, only devastating attack power.