User blog comment:Primeramizery/What could Mayuri be working on in his lab?/@comment-4207271-20130709084205/@comment-3230060-20130709133420

I disagree. Yes they were rivals, but with her gone noone can stop his experiments with poison.

She is a power house, but i think her ability has already been explained. The bankai your refering to WAS activated in the fight with Zaraki. And it just HAPPENS to be the time when he awakens his Zangpakto.

Whatever he is working on will help SS, if it's unohana or not, or he wouldn't be doing it.

Honestly i think it's Kira. Because he hasn't been mentioned since his injury. But that's just a guess.