User blog comment:Xilinoc/Ch. 579 - THE UNDEAD 6/@comment-2211792-20140508131732/@comment-24546844-20140508172249

Just posting something I wrote in another forum:

"I'm still confused about Gremmy's death, maybe he imaginated having the same power of Zaraki. Zaraki don't have imagination power so he wouldn't have it after acquiring his power, and as himself said his imaginated body wasn't enough to contain Zaraki's power and without his imagnation power he couldn't create another body or even his own body. Maybe that's why he just vanished. I don't think Yachiru is Zaraki's zanpakuto (which still haven't had a power explanation) also. Maybe she was absorbed by Sternritter Z. But if she is indeed Nozarashi Zaraki probably already knew that as he don't looks too surprised."

In my opinion he wanted to have Zaraki's power so bad that he lost his own in the process or something like this.