in a really simple and one-note term: stubborn. stubborn with their values, stubborn with their beliefs, stubborn with their causes, stubborn with their wants. characters who, when told that they are wrong, that they can't do something, that a situation is impossible — respond, unapologetically with "fuck you, i will". i love writing them fail; i love writing them cling with every ounce of their being to something that will destroy them in the long run; i love writing their decisions biting them in the ass; i love writing them sacrifice; i love writing them succeed, against all odds. most of all, i love writing them having to grapple with what happens when they're proven so terribly, horribly wrong. the sunk-cost fallacy is SUCH a fun thing to play with for me, and it gives me a lot of opportunity to see how that'll impact my characters and what they're gonna do about it. characters who toe the line between "selfish" and "self-sacrificial" with a knack for controversial choices that would likely result in who even knows how explosive of twitter discourse.

for a less pretentious answer:
‐ characters who are an absolute hot mess disaster of a human being. awful people made of more vices than virtues, self-loathing sad people who can't help but do more things wrong than do things right. 
- pragmatic women who are either desperately ambitious or desperately yearning to survive, bar none. women who have had to make difficult choices and roll with the punches, separating their personal feelings for what needs be done. women with a myriad of regrets but can't afford to process them as regret, not as long as something needs be done. women who desperately want to be good, but for some reason they can't — they don't think they'll ever be able to reach that Good they want to be.
- doomed by the narrative twinks. usually brooding, stoic, and serious. usually quietly idealistic, in love with the possibility of making the world better, whatever the cost, but they have to be in an unforgiving setting for this to work for me. men who are made so wholly undone by love — of a place, of a person, of a people, of a cause, etc. 
- fiercely, fiercely independent characters who want to demand change, pave the path for it in whatever way they have to. characters who are more prepared to die than they are to live, who imagine sunrises they'll never see, or believe they'll never see. characters who try to do the good thing, the right thing, the morally Correct thing for them, only for that to be disastrous, but fuck, is it the only thing they have left to believe in. but the good thing they see may not be the collective Good Thing as a whole.
- loyalist cynics with bloody hands; willing to be the bad guy, do the awful thing, do the morally reprehensible thing, because someone needs to do it. soldiers who have made themselves weapons, with nowhere else to go, no sense of self beyond a corrupt or cannibalizing system that has no love for them at all.