This is something that bugged me. If this addressed already sorry I am new to the forums.
Anyways the contract Wyll states he is to go after the heartless, and his handler says Karlack has no heart.
This is not true..... yes Karlack's biological heart has been taken out but the machine replacing her heart, functions like a heart plus perks. Therefore Karlack has a heart. The contract does not say the entity in question must have its original heart, but one without a heart. Since Mizora is clear of "heartless" is the lack of a heart and not heartless as in a cruel person to homicidal maniac.
So Mizora is the one breaking the contract not Wyll
Wish my character can bring up that little fact.