Hardest: Noel, Aya
Noel's difficulty just feels... out of place. Difficult for the sake of being difficult, when storyline wise IT JUST PLAIN DOES NOT MAKE SENSE FOR HIM TO BE. Up until this point, he has been trapped in an orphanage (where he was not allowed to battle), broken out by you, hidden in the railnet, kidnapped again, and had to be saved at least one more time, not to mention the fact that he logically should not have a team that optimized, given that he is on the run and hiding out in another leader's house. And yet this little guy is the one that gives us all trouble? [expletive redacted] he's the one that be saving everyone, not me.
Easiest: Charlotte