"I was born into a long line of knights. My house and all that crap. This title will be mine by inheritance when the time comes. I could spend my life eating grapes from a damn silver bowl and still be called "sir"! ... [But] there's no honor in accepting something you haven't earned! A knight shouldn't just be lucky enough to be born to some damn noble! A knight has duties. ...Responsibilities. "A knight is brave and true, aids all in need, and defends the weak from evil." I can't up hold that oath without honing my skills. Suffering hardship. All of that. How can I know courage if I don't face bloody death a bunch of times? I'll fight for the Shepherds until I've damn well EARNED the title of knight!"
SULLY. IS. A LADY. AND GAVE IT UP TO EARN A TITLE SHE WOULD GET ANYWAY. DOES IT GET ANY MORE BADASS. She fights nonstop and pushes the others to do it too. Her determination and willingness to better herself is incredible. She does what she says she's going to do. And she understands that you have to work for what you want, and isn't afraid of that. I think that's really admirable.
I think she gets a lot of crap because she seems like a one-trick horse, or a major Tomboy/Bokukko stereotype. And I'm not going to say that her issues don't get redundant. But Sully's a little deeper than that. Sully is a walking identity crisis, and a social commentary unto herself. And best of all, through the vessel of Sully's gender problems, we see that all of the Shepherds accept her for who she is, which is really what's important.
We'll start with her supports with Stahl, because it shows that her views of herself kind of throw people off:
Sully: I won't stop until I'm built like the bull!
Stahl: Ha ha! I'm sure you'll... Wait, you're the Bull in this scenario?
Sully: You got a problem with that?
Sully: But you know the others expect you to show me up someday. ... It's okay. I'm used to it.
Stahl: ...Er, Sully? is everything all right? You're getting weird on me.
Sully: It's just... People look at me and all they see is a damn woman!
Stahl: Um, okay? Not sure where this is coming from, but if I implied—
Sully: Not you, idiot. You treat me as an equal, and I've always respected that. I just worry that... Well, what happens if you do surpass me someday? People won't think it's because of hard work or skill or any of that. It'll just be another damn man beating a woman to the finish line again.
That's probably why she is always so obsessed with winning and gets really pissy when she loses--because every loss is damage to her reputation, and her reputation as a woman knight is already pretty precarious (not within the Shepherds, which I'll also discuss later, but to society in general).
Let me give you a personal anecdote about being a woman basically living in a man's world (I identify a lot with Sully even though we're nothing alike, and this is why). The fencing stance, as it is taught, doesn't accommodate women's hips. I know tons of women, myself included, who experience severe knee, hip, or back pain from fencing in a man's stance. The way our hips angle just does not agree with the rule to keep your front foot pointed forward; you really have to angle it in some or you're kind of screwed. Most women fencers do this naturally, but those who try hard to adhere to proper form? BAM, have fun walking tomorrow. You are literally punished for being shaped like a woman. After fencing I'd often have to just lie down on the ground and let gravity pull my left hip back into alignment (which hurts), and in that odd limbo-state of crooked joints I was physically neither man nor woman, as far as my bones were concerned.
And that's where Sully is. She is a woman, and knows it, and doesn't want to be treated like just one of the guys, as her S support with Chrom shows. She can be a "typical" girl in a lot of ways, which sadly we only see in her supports with Sumia since the rest are wholeheartedly devoted to her gender crisis: she wants to gush about horses and drink tea, and wants to hear about Sumia's love life (even gets kind of romantic about it--"And what are friend for if not to hear confession of a sultry midnight passion?!"--although she get super flustered when Sumia makes her talk about it first). And really, for all her obsessions with fighting and strength, she doesn't like the war. She and Sumia admit in their C support that world peace would be better because then they'd have more time for tea and horses. It's kind of adorable.
Stahl reminds us how she's physically a woman when she makes him shake her hand to make a point about his grip: "Well, yours is smaller than I would have thought... And really soft! It’s kind of nice, actually."
The thing is, she is insecure about herself and who she wants to be vs. who she actually is vs. who society wants her to be, because all of those are different. Look at her A support with Chrom: "...the other women decided to become a bunch of damn LADIES. Aw hell. Some days I wonder if maybe I…"
And Chrom is all OH NO YOU DON'T. He says he likes her how she is because he can speak to/fight her like an equal, even though this implies that the other women are not his equals (danger zone, here, but this gets partially resolved). And we see in her S support that this actually hurts her feelings:
Chrom: But I thought you liked being treated like one of the guys?
Sully: Gods bless it, no! I'm not! I'm a woman, too, dammit!
Sully always has to be true to herself. She's a "mannish" woman, but she's still a woman, and she doesn't like her attitude or her abilities to cover that up. But because of all that, she has a really hard time fitting in either sphere. So hard that she has Miriel study her to try and figure out why she just can't belong:
"Look, I just want you to figure out what's so different about me. I mean, I TRY to fit in, I really do, but something sets me apart."
And when Miriel tells her it's how she acts and talks, so she should change that, Sully get's pissed: "I've had people tell me this before! "You have to do this!" "You gotta act like that!" It never works! I pretend for a week or so and then just give up. Who says we all have to act the same, anyway? Who made all these damn rules?"
Her attitude is not an act. It's how she really is (perhaps deeply influenced by a childhood desire to keep up with the boys, or by her brothers, but still genuine). And society's gender roles are keeping her from feeling like that's okay. You know something all her S supports have in common? She never has to become more of a lady for anybody. All of her potential husbands accept her for exactly who she is, and even love her all the more for it. (While this is definitely contrived in some cases, as many S supports are, some of them feel really genuine, like Stahl's. And I think Chrom says it the best, for once in his life--he needs a wife tough enough to help him rule a nation. And she's like BITCH I'M TOUGH ENOUGH FOR ANYTHING. In fact, she proposes to him.)
The part where it can get grating is where gender becomes the focus of all of her supports (except Sumia's), and it detracts from any of the other aspects of her character. But in this I like to see her as something of a social commentary. While Sully struggles with her identity, the other characters are helping her out by pointing out that it's okay to be different, or that they like to be with her just the way she is. And while it doesn't develop Sully any, it develops the Shepherds as an organization.
My example for this is her B support with Ricken, when Ricken says he's discovered a spell that turns a woman into a man and assumes she'd be all over that:
Sully: If anyone else had said that to me, I'd make them eat their own guts. Look, Ricken. I'm fine as I am. I'm not looking to switch sides.
Ricken: But I heard you say before you hated not being taken seriously because you're a girl.
Sully: Right, but the problem isn't me. It's that other folks are small minded. It's a stupid way to think, and I aim to prove it. I'll outfight every man on the field, but there's no point if I don't do it as me.
At the end of the day, Sully has to do Sully. Yes, her conflict is really hammered in, and it detracts from making her a character that is truly fleshed out, because only one aspect of her is ever explored. But the conflict in itself is handled well, in my opinion, and this is an age where this conflict is coming up a lot for a lot of women in a variety of ways, and all that will need to be resolved well too. So it's good to have a small example in the media of it.
Unrelated, I love that she says "DAMN" if she dies in battle. Because I'm totally thinking it, and if she says it I don't have to.