User blog comment:Apocaylpse06/Ichigo Kurosaki's (New) Zanpakuto/@comment-2048489-20110818000353

Reasons I believe it's Zangetsu: 1) Sword has the same style of look as the previous form of Zangetsu: a massive sword designed for brutal beatdown 2) This was metioned in a filler arc, but Zanpakuto evolve with their Shinigami. It was not stated HOW they evolve, so we can assume that a Zanpakuto will change as the Shinigami grows stronger. I think Kugo even confirmed this during the chapter he was talking how a completed Fullbring was a dead end 3) Getsuga Tensho. We all know Engetsu can use it, but even considering that only one or two Zanpakuto that can use it. 4) Other reasons that have already been stated