The sheer look on Alucard's face when he finally kills Anderson. While Alucard has gotten angry a few times, this was the one and only time he was literally reduced to a screaming rage and attacking someone without any of the sadistic joy he usually did. Right before breaking down in front of everyone, crying and cursing Anderson and even himself for their mistakes. He even begins sobbing at the end
Alucard: YOU AND I ARE THE SAME! (everyone gasps in shock of what he said) You are me... I was just the same! Don't you understand, this is how I became what I am!