How do I begin to explain Grace? Do I start with the fact that she's a subversion of a horde of most popular female character's tropes and that it was her conscious choice? That she's a representation of a survivor, and not only she didn't let her abusers ruin her life, she also changed herself from a victim into a healer and mentor? That she's so badass, she literally fought with the hostile universe's expectations of her and decided to be better than that? She's so much more and she never stops getting better.
Grace is a succubus, beautiful and deadly demon, born to seduce mortals. Her mother sold her to baatezu - the devils, mortal enemies of tan'nari - demons. While all of them are creatures of evil, tan'nari represent chaos and destructive impulsive desires, while baatezu is an order and calculated cruelty. Their main idea of pleasure is watching others suffer, and torture - physical, mental and emotional is their main form of art.
Now the awesomeness starts. Grace freed herself with the power of her creativity - she wasn't saved by someone else, she didn't escape by chance - she out-witted proud devils in the contest of improvisation, using tan'nari natural chaotic nature. It wouldn't make her less awesome if she'd just ran away or tricked her slavers, but it shows Grace's main strength - she takes disadvantages that the world gives her and throws them back with a double power.
So how did Grace act after living through a literal Hell? Had she closed herself to the world, filled herself with bitterness and hatred, tried to bring vengeance and cause others pain that she herself was unfairly subjected to? Nope, because she's not your average Brooding Hero. She joined Sensates - philosophical faction, which believes that the universe is meant to be experienced in as many ways as possible. All that life ever showed her was cruelty and torture, but Grace thought "There are should be good things in this life, and I'm going to find them even if I wasn't supposed to."
This is incredibly important message - even if you were born or subjected to painful disadvantages, even if you were hurt so badly you think you're broken, even if others or you yourself think you're imperfect, you still deserve good things. Your "nature" and your past does not define you. You don't have to accept crappy life, there are good people, healthier environments, and just so much more to this world out there, and you deserve it all.
As a succubus, Grace was designed to be a pinnacle of Femme Fatale trope, probably the most old and popular archetype of female characters - a treacherous seductress, who uses her beauty and femininity to kill men with a mere kiss. The idea in this trope is that main and the most valuable trait of a woman is her appearance and sexuality, but sexy women use it as a weapon.
So Grace took universe's expectations of her and with her quiet elegant irony turned it upside down - alongside with ruining virgin-whore dichotomy. She opened a "Brothel for Slaking Intellectual Lusts".
Fall-from-Grace: The brothel is intended to slake the lusts of even the hardened intellectual. It is designed to stimulate the mind, to heighten one's awareness of themselves and others, to create new ways of *experiencing* another person.
The Nameless One: So this establishment just encourages intellectual fencing rather than, uh, well the *other* kind of fencing. So the Brothel is a school of sorts?
Grace: Yes. I hope that by learning the art of language and its subtleties that the patrons and the students here may learn more about themselves. One is only as limited as their command of the language. To be able to employ language to evoke emotions in others is a tremendous skill.
So it's basically place where you can talk about anything you want and learn how to communicate with other people. Do you get it? She opened a therapy and life-coaching center in the middle of Sigil. How awesome is that?
Apparently not enough for Grace, because she gets even more amazing. She's a cleric, and clerics in DnD get powers from believing and worshiping a deity and the ideals it represents. Grace gets those powers from believing in herself and self-growth through exploring the world
I believe in *Experience*. I believe a person may be changed - for better - the more of the multiverse they are allowed to perceive and the more the multiverse is allowed to perceive them. I suppose the best explanation is that my faith allows me to *see* things differently. When you see the multiverse in such a way, you learn how to 'change' things - mending wounds, seeing a person's heart, and so on - just by willing them to happen.
GRACE YOU ARE MY HERO, this is better than even Sailor Moon's power of love! But wait, it gets even better
TNO: Do you believe in Experience because of what happened to you with the baatezu?
Grace: I think it is because I am content what I have become, and I do not think it would have been possible without experiencing the multiverse as I did.
TNO: I don't think it has anything to do with you experiencing the multiverse... I think it's how you dealt with the experience that was important. I think there would have been many others who, when subjected to the experiences you were, would have crumbled. You *learned* from it, and you became stronger. It shows great strength of will and of character. And I admire that about you. Not only the strength, but the ability to see such horrors as a way of becoming a better person takes a strength *few* possess.
She not only didn't let her traumas to ruin her life and define who she is, she used it to her advantage to help her have a better and unique perspective on the world and other people, so she can help them.
I also want to mention that isolating periods of abuse and other traumatic events, viewing them as a completed limited experience which can be used to improve yourself, and recognizing that it's not your fault, but part of the world's imperfections which should be fixed is one of the most useful methods in therapy. And Grace came up with it on her own and now she teaches it to other people. Grace let me cry over how perfect you are
But! It's not her happy ending or even the end of the way. It's Planescape: Torment, and this game never sugar-coats things. Her name is Fall-from-Grace and she took it herself. Why would she choose it?
Grace: I have fallen from my people... some would say risen from my people, perhaps, but 'fall' *feels* more right to me. Does that make sense?"
TNO: Yes, it does. After all, 'fall' carries with it an underlying sense of loss.
Grace: Yes... perhaps that is why it felt as it did. I... came to terms with the loss long ago, but the name has remained.
This issue is rarely talked about, but it's very important. Many abuse survivors question themselves and still feel longing for the lost roots, even if they realize it was unhealthy. It's completely normal and natural. Everyone wants to have a sense of belonging, and losing an identity and all what was connected with it is still a tough loss even if this identity was destructive. It does not mean you were wrong to change or that you should stop and give up.
Many characters throughout the game say that Grace haven't changed, accuse her of pretending, having an ulterior motivations to use the protagonist (it's all bullshit of course). But it shows that she'll never be really accepted, but she doesn't let it to bring her down and still helps people who are suspicious of her.
Now a little about her narrative. She's a chaste succubus and a romance interest. In any other game she'd be just a succubus with a gimmick. Here, those tidbits of the dialog are probably the dirtiest part of the romance. She's not an exotic trophy for player to won. She's not a hurt damsel to be saved. Player can't "fix" her with a power of magical penis True Love. No matter what a bastard of character you play, the game doesn't let you question her decisions or treat them disrespectfully. I shouldn't have to even mention it, but I've seen it happen in so many other instances and all forms of media, it feels like an achievement.
In conclusion, Grace is very deep, fantastic character with many layers, but for me her main theme is bravery of exploring and experiencing your life, the strength of her choice to not let the world define her and her search for herself even if there's no easy answer, accepting who she is now, but always trying to change for better.