I had the idea of an unfriendly girl who never develops any romantic feelings for anyone and instead grows to simply be less of a wannabe loner(like Reiji). The catch is that the reason she pushes folks away is cause she's a trained killer who gets kicks out of killing and inflicting pain. Despite being fully aware it is wrong and hating the fact that she knows and still likes to do so. Thus she takes out her pent up needs on Shadows instead. She's not nice, she isn't dateable, she's technically insane and dangerous yet she still wants to be normal and save lives.
Would that be a good enough rough idea for someone to still enjoy a deeply flawed character?