Most of all, Deadache is being that has had it's ability of living normal life stolen from her. She's been forced to live by the sentence kill or be killed, and it has been her lifelong guideline for so long, that it's mostly deadened her normal feelings.
Deadache isn't completely emotionless, though. She's mostly cold and almost always has unwavering control over her own mind - and being extremely controlled to the point of insensibility is what she aims for - but deep down there, under the steady and at times almost lifeless behaviour, are feelings. They're quite weak, but they are, and at times they even manage to break through the rationality and logic Deadache treasures. And at that point, she's at her worst - Deadache knows how emotions work theoretically, but she has no idea how to deal with them in practice when she's the one to feel them. She's capable of feeling something quite normal just for a little while, until those emotions get as twisted as Deadache's mind is overall - and at that point, those emotions may infect and darken the mind of that one, who has caused her to feel in the first place. She steals minds, she puts them in chains they possibly can never free from, but actually just because at that point she can't just stand the idea of that someone leaving her. She wants to own, by stealing someone's thoughts and free will she wants to make sure she won't be left alone.
Being rather delusional but still very intelligent Deadache is of that classical fictional sociopath -type. She's cruel and sadistic and only cares about her own well-being (not too much of that either, though - she's not actually narcissistic), and everyone else is quite insignificant for her. Honestly, the whole idea of living is quite insignificant for her; her view of living is just to survive from one day to other, from year to year, just to get through the challenges life throws you into. And all this without any greater purpose, just because.

Question may arise, why? What has caused this madness, this cruelty that seems not to know any borders?
Deadache was born to be a war dog. The fact is, she didn't choose to live like this, not at all; that decision was made for her long before she was even born. There's no psychopathy in her genes, that blood-thirsty monster is what life forced her to be by stealing her changes in the very beginning. There were only two opinions given: Do as said or die.
And Deadache choose to live. Till these days something in her corrupted, tormented mind, has kept the "kill or be killed" -phrase as a basic, something that needs to be obeyed in order to survive. A subconscious feeling in her head tells that she can't trust on anyone, that if she does, she'll be dead. She's not living the war anymore, but the years of exploding bombs, painful screams and exhausting battling, still live their life in Deadache's mind, keeping sure that she won't ever feel like normal person, that she can't really even wish for the normal or even somewhat normal life so many else around her are enjoying of. She's an outcast, once and for all.