User blog comment:Xilinoc/Ch. 665 - The Princess Dissection/@comment-2120712-20160310143907

I will say once more what I have said on reddit:

This is the one. Urahara not Shunsui is the one I wonder why he never went bankai against Aizen during the Fake Kurakara Town arc unless his bankai cannot rewrite the Hogyoku or its now likely permanent connection to Aizen. Shunsui's bankai became useless against Aizen the moment he entered the Chrysalis phase.

This also means that we have a confirmation of Urahara's zan theme. Its low level reality or molecular manipulation. Not blood (my original thought on his zan was reiatsu infused blood). My guess in shikai it’s limited to energy manipulation and constructs; and moves up to the very fabric of reality or the atoms that make up whatever it is touching. The limit to what it touches is a smart idea otherwise Urahara would be truly broken and I wonder what was Yama's response to seeing Urahara's bankai during the captain proficiency test. The blank canvas statements from chapter 664 were a big hint to his bankai abilities.

Oh, I noticed something about the Scientist warriors of bleach. Their abilities are geared around some aspect of change or modification. Mayuri's modified bankai has limited evolution (his default bankai uses poison based on his blood) while his shikai disables the nerves responsible for movement (which is taken to another level with his fear factor 4 ability), Kisuke has low level reality manipulation in bankai while in shikai he has energy manipulation, Aizen controls the five senses in shikai, and Szayel has medical based voodoo doll like abilities as well as the ability to rebirth himself from his infected opponents. Mayuri, movement; Kisuke, reality (though his bankai is acting more like a surgeon); Aizen, perception; Syazel, form. In fact together they kind of represent surgery in general. Aizen and Mayuri, movement and senses are dulled; Kisuke, the actual surgery; Szayel, the end result. Askin seems to represent poisons and vaccines (his adaptive evolution making him immune to attacks after experiencing them).

Perhaps that is the theme of Kisuke's zan: Surgery, filtered through low level reality manipulation.