Board Thread:General BlazBlue discussion/@comment-30711988-20170203165111/@comment-30711988-20170326084841

Well, some part of Terumi being left in the Unit may be an explanation for that, and is actually the only explanation for Terumi's sudden personality change when he became Susanoo.

And there's a fact that supports your theory: even after Hakumen was "killed" with Hihiirokane, some part of him was still left in the Unit. Maybe it's actually impossible to completely leave it once one is recognized as Susanoo?