[Whewt22]

The second personality is a hollow, because its a hollow rofl enough said. Kisuke used the same method Aizen used to turn the Vizard into hollow. Accomplishing Kisukes task of getting out of the hole kept the hollow tame for so long. I think Kisuke noticed this but didn't want to reveal to Ichigo that he had anything to do with the Vizard so he contacted them, and told them he has the samething going for him as they did. They took him in, and supressed his hollow instead of Kisuke.
All part of a master plan...