Board Thread:General Discussion/@comment-24185694-20140827001813/@comment-1268838-20140827234513

Despite her impressive feat in the fight with White, I'm not so sure that Masaki is necessarily captain-level.

For one, Aizen stated that White "chose" Masaki as a Hollowfication target. Against those run-of-the-mill Shinigami and Isshin, it seemed to be going for the kill; it went all out with its blade arms and Cero and whatnot. It merely bit Masaki, which for all we know, is how it transfers itself (i.e. the Hollowfication poison).

And while it's true that she got a good shot in, Tousen more or less implied that it chose to self-destruct not because of the damage it sustained, but because it had successfully entered Masaki's soul. I think that it is entirely possible that it was an empty shell that she damaged, assuming that the transfer occurred before her attack and not after.