Unpopular opinion right here. Very unpopular. I don't hate him though,I just have a huge disliking for him and I don't see how he's so cool and such. That and there is nothing special about him. Oh yeah. He's a demon. So is Claude yet a lot of people hate him.
For me it is Creed Diskenth. This guy is crazy, creepy, narcissistic, "superior" to all, and obsessive!
The main character Train was an assassin in the organization Chronos along with Creed. Train's parents were killed when he was young with left him feeling cold and indifferent until he meet Saya. She opens his eyes and helps him see that he has choices as whether to kill his victims or not. He leaves Chronos but Creed Diskenth resents the way that Saya changed the elite assassin's life, and MURDERS her.
Then the rest of the series we see Creed with this look below on his face every time he thinks of Train. He becomes obsessed with making Train kill again and his ultimate goal is to rule the world with Train. He becomes madami and madami insane as the anime progresses.