User blog comment:Malicesu/Concerning Grimmjow/@comment-24913480-20140903084014

Remember the mysterious character that bifurcated Quilge Opie and later on entered Kisuke Urahara's tent while he was talking to Ichigo, just before he went to the Soul King's Palace (chapter 518)? Many readers believe that is Grimmjow. Also, in that same chapter, Urahara stated he made a contract with him. I believe it is something along the lines of: Grimmjow helps the shinigami fight the Quincies and in return gets to fight Ichigo again. Only speculation, I know, but quite possible.