The OVA obviously answers the thing that disturbed him on the episode in the season one with Satou. Which I say, if your head's have been slashed off or got ripped on some accident that could actually make you die, your own body only owns you. There's no "new" personality or mindset when you saw your own head regenerating because obviously, you died anyway. And Nakamura Shinya's multiple IBM is quite answering also to the scene of Izumi where she thought that Kei (or Ajins) can't produce multiple IBM at the same moment but made it really possible and I really like the wholecircle of the story. Although I know the OVA is incredibly short, probably the ongoing season two answers the remaining questions and revelations are always ahead. We'll see if Tosaki's past with his fiancee will get a screen flashback too.