This is something that recently came into my mind. Yagura was the fourth mizukage and jincuiriki of the 3 tailed beast. According to the manga there is strong evidence that while alive yagura was manipulated by someone else. The fifth mizukage went as far as suspecting shisui's eye technique, kotoamatsuki, could have had something to do with this. The issue? Well, both of shisui's eyes have been accounted for and it seem heavily unlikely akatsuki actually ever had any of them. The first eye as we saw was in the possession of itachi and he had that crow thing keeping it safe. It was not apparent that anyone in akatsuki knew about it either, let alone tobi. the other eye was held by danzo and we do know he was not quite akatsuki's ally.
So it leaves, the question, WHT? Did shisui while alive inflitrate akatsuki and controlled the mizukage at tobi's request? Or did itachi or danzo in some dealing with akatsuki (akatsuki was a mercenary group for hire, it is entirely possible that was some form of payment) went as far as to manipulate the leader of a nation? Maybe shisui was a member of akatsuki in the same manner as itachi....
So it leaves, the question, WHT? Did shisui while alive inflitrate akatsuki and controlled the mizukage at tobi's request? Or did itachi or danzo in some dealing with akatsuki (akatsuki was a mercenary group for hire, it is entirely possible that was some form of payment) went as far as to manipulate the leader of a nation? Maybe shisui was a member of akatsuki in the same manner as itachi....