There are a couple of characters I've seen that I personally relate to a lot more than I'd like to admit.
Reki from Haibane Renmei is probably the most relatable character to me. Even down to our methods of CTB being the same.
She puts on a fake persona, trying to help other people to atone for her own bad personality; but it's just an act in the end. She's not a good person, but she still tries to act like one to help others. In a way living vicariously through the improvements she helped bring to them, while also feeling secretly bitter and resentful she can't succeed like they do at the same time.
Watching Reki's behaviour was so uncomfortably like looking in a mirror. She's manipulative and cold, but she does seem to genuinely care as well, she hasn't entirely lost her humanity but it's pretty close. It makes me wonder if whoever wrote her character had BPD themselves, because the things that she does and reasons why are so similar to mine which come from my BPD.
Akemi Homura from Madoka Magica is another one I relate to a lot. Homura is similarly not a good person, she only cares about the one person in the world she loves, and she just wants to be able to live with that person, but she suffers countless days of torture only for the person she was trying to save to abandon her in the end anyway. Her actions in Rebellion make sense because she is just fundamentally a selfish and bad person.
Something that really hit me when watching this show was specifically the scene when she said to Madoka (after defeating Walpurgis together and them about to turn into witches because of their despair,) "why don't we just become terrible monsters and ravage this world together. Wouldn't that be nice?" She only cares about being with Madoka, she doesn't care about anyone or anything else, but when Madoka asks Homura to kill her so she doesn't become a witch, it's like it suddenly hits her that while she would find that "nice", Madoka just isn't that kind of person. so she begrudgingly kills her, respecting Madoka's wishes and shouldering all the burden for her.
I have a kind of similar attitude to Homura: If the people I love would be evil with me, I would give up on trying to be good and just do it. I would love nothing more than to empty out all the suffering we have had to endure over the whole wretched world, seeing everyone else hurting just as I was made to. It would be so cathartic; but I know my loved ones wouldn't find that "nice" like I do. I am not a good person, I just pretend to be as best I can; but my loved ones are actually good people, they aren't vindictive and cruel and spiteful like I am. So I can't give in to that impulse and inflict cruelty to others no matter how much cruelty is inflicted on to me, because I know none of them would join me in reveling in it. So I have to keep pretending I'm not a bad person for their sake, and suppress my manipulative and vindictive thoughts and behaviours as best as I can.
This all probably sounds extremely melodramatic and self-absorbed, but being the subject of the thread I thought I'd try to explain why I like these characters the most. I'm not good with words so hope it made sense.