"Redemption arc not forgiveness arc" is something so important to me. (Ice king/Simon ramble ahead)
Everyone who's willing to work towards redemption is allowed to redeem themselves, even if only for themselves and the rest of the world still hates them. No one HAS to forgive that person. And other people ARE allowed to have mixed feelings about them trying to redeem themselves, some people may never forgive them!!!
All this to say. Ice king to Simon transformation/redemption arc.
There's princesses out there that he's kidnapped that won't forgive him. There's princesses who are still uncomfortable being around him, especially alone. There's princesses who understand that this is Simon now and no longer Ice King, but still don't feel fully comfortable with him even if they forgave Simon. There's princesses who straight up HATE that man even if he's Simon now, because of what he did to them as Ice King. There's princesses who fully forgave him and hold no bad feeling towards him.
Not just princesses either, probably whole kingdoms worth of citizens who don't trust Simon because Ice King took their princesses, or neighboring kingdom's princesses. Maybe even just heard about the kidnappings and got weary.
I wouldn't be surprised if it ruined ally ships between kingdoms because one leader forgave Simon while the other didn't. Or the citizens of a princess who had been kidnapped but she forgave Simon, were still mad and barred him from entering anyway.
It doesn't matter how much Simon has changed from Ice King, how much he apologizes and shows that's not who he is. There'll be people who don't fully forgive him, aren't comfortable, or hate him completely.
Redemption is not forgiveness












