Tell me this, If he merely healed wouldn't he have the same body? In the sequel he has a different body thus making the theory of him being reborn factual.
What exactly proves that in the sequel he has a different body? Ken never had any distinctive trait to begin with, aside from his white hair. The sequel takes place after 2-3 years and I think that he now is 22 or 24, not sure about the exact age. His body grew perfectly naturally, he could have even dyed his hair seeing it black and white. Just because his body looks different to you, it doesn't mean that they created an artificial one and then they put his brain somehow in it. Besides, in the manga, Arima chose very carefully to pierce Ken's eyes and after that his brain. In either of our scenario, his brain must have remained intact, functional. That being said, if his brain remained functional to begin with, then he could have very well used his old body. Ken's body was never destroyed, and that was exactly Arima's aim; to make use of him afterwards.
