Either Makima is human who has lost a good deal of her psychological humanity as compensation to the devils or she was a psychopath to begin with. In fact having been that since childhood seems more likely, and it's exactly why she keeps getting very good deals from the devils, allowing her to become so powerful. Devils recognise her for what she is, a monster, and they don't demand eyes, limbs, or kidneys from her, instead they are delighted to help her, knowing she's enjoying killing humans as much as the devils themselves.

Quote Originally Posted by MFauli View Post
I'm still hung up on the "violence devil". Some weeks ago, you guys said to me "no vague concept devils" when I talked about it, now we have confirmation of vague concept devils existing.
I'm starting to suspect the author never created that many rules for the world of this series. However, one thing that I'd consider very, very likely, if I still wanted to imagine the rules that might not exist, is that there are probably multiple devils of the same kind around. Perhaps the more something is feared, it doesn't necessarily create a single stronger devil, but it would primarily create more devils of that kind. Something else then allows an individual devil to get stronger and stronger.

We already know that if a specific devil is feared, it can get stronger pretty quickly; remember the hotel arc. If you think about it now, the Gun Devil we keep hearing about is quite smart, creating networks with enticed mafia goons and definitely corrupting people even outside of mafia, including the Public Safety agency, because, like I said before, how the strike against Makima's group earlier was arranged, it required inside information. So, as far as I can see, the Gun Devil has been fully intentionally creating a situation where it's feared more and more globally. Yet I bet it's only one of the many gun devils (unless it has eaten the rest over the years). People might not have recognised it before it was already helluva strong.