Enemies to friends can work, DBZ does this better but even that series has some iffy ones hell even Naruto does it better and that has some egregious forgivness Cough Pain Cough Obito. The issue isn't forgivness that's a fine lesson it's the execution. It would feel more organic if over time the nobel changed his ways, by seeing the hero as an example comparing and constarsting his own life and values and deciding to take a different path. The 180 revesal feels insincere, it leaves the reader with a sense of whiplash and does nothing to endear the character to the audience.
Also I have to say Cross is badly written. Being kind and compassionate isn't weakness but it is a problem when it feels like parody. Writing a character this way can make them feel flat especially when forgivness comes without either trying to understand the person or any internal struggle it makes them feel less relatable, less human turning the audience away in turn.