User blog comment:Njalm2/Fanon Canon - Grimmjow's Espada!/@comment-2089817-20150116144217

In an Espada ruled by Grimmjow, who doesn't probably care much for hierarchy so long as they are beneath him, I don't think there would necessarily be a clean number like 10 anyways. 13 is probably the number that just happens to be how many end up following him, but what Nanja is trying to do (at least from my viewpoint) is demonstrate the idea that Grimmjow's Espada is not only different but a reflection of his personality; that being that his sense of rivalry can even be a bit childish at times, to a point that he'd have thirteen merely to flip the bird to the Gotei 13. Aizen's Espada was one of efficiency, he decided upon a clean number of ten because ideally, he wanted ten Vasto Lorde, which would've been just enough to topple thirteen Captains. It was a reflection of Aizen, in that sense. With that in mind, Grimmjow's Espada would therefore be a reflection of himself and a different number of Espada is definitely a possibility. I say give this a chance, guys.