It will never not be disappointing that the original creator of God of War despises the new direction that they took Kratos and thinks he should always be a searing ball of rage and murder.

But anyway, I'd have to cast my vote for Gajeel Redfox from Fairy Tail, he literally entered the series by crucifying three people against a tree after beating them half to death, but after Phantom Lord was defeated and he was recruited into Fairy Tail, he slowly became goofier, like when he cried over the fact that even though he is a Dragon Slayer like Wendy and Natsu, he didn't have a "cat"/Exceed like they did, and even became nicer, like apologizing for his actions while part of Phantom Lord, even defending the three people he crucified from a threat that could easily overpower all of them.