It's Mayuri. He's a prisoner in SS because he's too dangerous to society. Urahara needs his help. I'm SKEERED, MOMMY. *shivers in all kinds of good ways*
Thanks and roses as always go to Spacey and the spoilers and summaries as they happen can be found at his awesome forum here.
ETA: Lizzie is telling me that Mayuri in this scene looks eerily reminiscent of Uryuu when Uryuu was a prisoner in the 4th Division building. The clasped hands, the handcuffs, the nerdy look. There's something oddly sympathetic about Mayuri--like he's a boy genius gone bad. Kubo is playing with "what is EVIL" again.
ETA again: ananosa has added some text and pictures to the Ishida essay here.