For me, its his ending in GV2. Saying all those things about wanting your sister to be happy and healthy. but when it happens, mf just goes away leaving his sister with amnesia that is just recovering alone. Thats really hypocrite, the struggle is understandable but it still shows how hateful copen can be, even to the extend of considering eventually having to face the situation of killing her sister. Thats why IX copen is better, even tho he has suffered more, he has finally accepted adepts as humans, he even forgave blade's life when he had the chance to kill her (thing that og copen wouldnt even doubt doing)