I just hope the author is not going to redeem that east demon Lord: the least they could do would be sealing him with the help of god, but I'm the kind of person that likes to make sure I won't be bothered by the same thing twice.
But, you know? I feel a bit on the angry side: everything points to Rene being reborn just because his demon grandpa needs someone strong enough to get rid of that other demon... I hope I'm wrong, but.........