Tharja from Fire Emblem: Awakening
At the core of her character, Tharja is a prime and even obvious example of a borderline character. The most obvious trait is that her favorite person is the player character, default named Robin, regardless of their gender. This comes off in a sort of creepy way, of course, with Tharja stalking Robin and able to cite on a whim how many books Robin read the previous day and how many times they turned over in their sleep.
When called out by Robin for this behavior, Tharja removes herself from the conversation almost immediately, returning some time later and acting far out of character. She tries to make pleasant small talk with Robin, offers them their favorite flavor of pie that she cooked herself. The change in personality is so dramatic that Robin becomes concerned, both for her current state of mind and whatever “plan” she’s cooking up for them. When questioned about it, Tharja denies she’s acting any differently, but Robin tells her that she shouldn’t have listened to their request to be “normal” - which wasn’t a request at all, simply a comment Robin made in way of concern for how Tharja was behaving compared to their other “normal” friends.
It is implied at more than one point that Tharja cursed and/or has considered cursing Robin to fall ill or behave/appear in such a way that other people stay away from them or that Tharja has no choice but to take care of them. However, this is never confirmed to be true, and Tharja even worries, when Robin does collapse from a bad fever, that they may accuse her of cursing them, to which Robin assures her that they would never think that. Tharja also feels very threatened by other characters getting close to Robin, to which she considers cursing them as well, though to herself and the threats never come to fruition.
Even when Tharja manages to direct her love somewhere else, she always seems to make sure her partner knows that they are only second best to Robin. In the instance of marrying Henry, she makes him promise to sacrifice her if it means saving Robin, if the two of them were ever in danger. With Libra, she tells him that he is the ‘second most important’ person in her life, right behind Robin.
Tharja seems to have difficulty being secure in her relationships as well. On event tiles with her partner, she says things to them like how they better run in the afterlife if they die before her, and that, if they cheat on her, the ‘consequences’ will be dire, despite the fact that Tharja is heavily implied to not even be able to cast curses at all; given that every time she tries, she fails, and anything she does manage successfully is mundane and not harmful, or in one instance even beneficial.
In conversations with her friends, she is seen multiple times to threaten them with a curse or hex, even lying that any alignments they have are entirely her fault. She does this in an attempt to get that person to hate her and avoid her from then on, but since it usually fails, she later reveals, either to herself or directly to the person, that she never actually cursed them.
Despite this, she is shown to be empathetic to the needs and emotions of others. Upon learning that Nowi’s parents are dead, she tries to play it off that they are just far away and her magic can’t find them because of this, in order to spare Nowi’s feelings. When she later finds Nowi crying because she may in some instance know the truth, she assures her that in the near future, Nowi will be extremely happy and loved, even more so than she feels now.
When confronted with the inferiority complex and severe anxiety of her daughter, Tharja assures Noire that she does love her and wants to keep her safe, hence both her and her future’s self’s decision to not teach her dark magic. Noire reveals that the future Tharja made a talisman that, whenever held by Noire, alters her personality in a way that, while it does make her rude, also temporarily erases her anxiety and makes her more confident, allowing her to be a capable soldier and defend herself in times of trouble, considering Noire actually grew up in a very dangerous and unstable time in the kingdom.
Perhaps on a smaller scale, Tharja has cursed both herself and others so that she appears invisible to them, under guise that, in battle, she doesn’t want them trying to protect her. When Frederick still takes a blow on her behalf despite this, she gets angry and snaps at him, demanding to know why he would do such a thing despite not knowing she was there. When soldiers inevitably die in battle, she removes herself from camp and regrets not doing more to save them, showing that she feels extremely responsible for the safety of everybody but herself.
All in all, Tharja, while she doesn’t display all borderline traits, displays quite heavily, unstable relationships, unstable/easily manipulated sense of identity, intense emotions (obsessions with Robin), problems with interpersonal functioning, poor impulse control, engaging in dangerous or risky behavior (dark magic), easily angered, unstable emotions and mood swings, and overall, these behaviors and feelings impair her interpersonal functioning and social life within the army.