Transgendered characters are rather rare in comic books. Sure there’s the cliche of Superman waking up as a woman one morning and Wolverine being changed into a woman by a fellow mutant; but neither of them were actually transgendered. Xavin from Marvel’s Runaways actually is.
Xavin

Born male, Xavin is a Skrull Prince and promised at a young age to marry Karolina Dean in order to make a treaty between the Majesdanians and the Skrulls. (Interestingly enough, Karolina’s parents always thought this would fail and set the marriage up for failure.) Xavin was in training to be a Super Skrull and idolizes K’lrt, the infamous Super Skrull who’s a frequent foe of the Fantastic Four. Like K’lrt, Xavin can mimic the powers of the Fantastic Four; however, she can only do one at a time and loud noises break her concentration.
Xavin comes to Earth to hunt for Karolina in secret. When they first meet, Karolina tells him that she’s not interested based on him being male. Xavin then transforms into a human looking woman to please Karolina. She tells Karolina that for a Skrull, changing skin is like changing your hair color or outfit.
However, Xavin’s ability to change form and sometimes shifting into a male form, especially when fighting or intimidating a villain, causes Karolina (and the reader) to have some doubt in how transgendered Xavin really is. In Runaways Vol 2 #8, Karolina and Xavin are arguing and in heat of anger, Xavin shifts into female form. It’s at this point where Karolina and the reader start to believe that Xavin actually sees herself as female.
Sadly, just when readers were hoping for Xavin’s storyline to expand, Xavin has been whisked away to other parts of the universe pretending to be Karolina. (More of this intergalactic strife.) While I’m sure this won’t be the last we’ll see of her, I do worry that we won’t see Karolina and her reconcile.

Karolina and Xavin kiss one last time.
Time to stop asking where all the women reading comics because here's one, right in front of you. Reviews and general comic book squeeing by Erica McGillivray (and a few others). I love She-Hulk, tiny baby polar bears, and a good book.
Xavin might not really care about gender. That would make her transgendered still, but not transsexual.
That is definitely a good point. I do think it’s hard to pin down a gender identity for a shape shifting character, especially one from an alien culture. And Xavin hasn’t had that much time in comics for fuller character development.
I think that Xavin is an amazing character and well though through, although i was really sad when she leaves Karolina im still happy that they love each other so much.
@Mack — I’m hoping the Runaways get picked back up and they can reunite.
i know i am too i love the runaways so much ^^