Thanks, everyone, for their feedback on this matter. After much thought on the matter, I decided I should make my STO character openly transgender, and tried to come up with a backstory that might help explain why transgenderism isn't quite so visible in the Star Trek universe. To that end I've written a speech my character could've given upon graduation from the Academy, although I'm not yet sure why she would give such a speech. I'm not quite so arrogant as to presume my character was the class valedictorian, after all. ;)
At any rate, this is a very early draft, so comments and critique are welcome.
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In 2385, my parents received a diplomatic assignment to Earth, and we moved to Seattle, close to my grandfather Jace. I was terrified of the change, as up to that point all I had known was Betazed. But the moment I met my Grandpa Jace I fell in love with him, and I didn't want to leave his side. I remember browsing Grandpa Jace's library which included a number of novels written in the 20th Century in the curious genre known as "science fiction." These novels puzzled and unsettled me. Some presumed there was no other sentient life known, but humanity--and the notion chilled me. But almost all of them were fairly unscientific on some level. Although most of the authors demonstrated a basic understanding of scientific principles, eventually the authors would introduce some made-up conceit, and often that conceit would prove vital to the storyline. Grandpa Jace finally explained it to me in a way that cleared up all my concerns and gave me fresh appreciation for the books. "They're not really about sceince," he said in his gentle yet deep voice. "They're about human beings. They're about how we'd think and act if things were different. You could say they're thought experiments for the human condition. The only reason why science fiction is no longer popular is because science fact these days change us faster than authors can keep up."
I think it was that insight of his, coupled with my affection for him, which led me to trust him with a secret that, today and for now on, will never be secret again. You see, my fellow classmates, I was declared a boy at birth. On Betazed transsexuality is very rare for reasons that I still can't quite explain, even after trying to find an answer for much of my life. But other species, including humans, have transgender behavior to one degree or another. Perhaps it's my partially human heritage that accounts for this. But the few times that I tried to tell my parents that I thought I was really a girl, they would tell me that I was plainly mistaken--although with much unease on their part. Grandpa Jace was different. His best friend, I found out, was declared a girl at birth but proved to be a boy. He also told me that Earth medical technology could help me grow up to be a woman. He introduced me to his friend, and he helped me understand myself and to come to peace with my understanding. But still, I hid all this as well as I could from my parents, certain they would not understand.
Then puberty began, and with it, my paracortex developed--and between the distress of testosterone and my unmastered telepathy, I lost my ability to keep my true self a secret. My parents reacted harshly at first. After all, my family includes members of the Fifth House, and parents worried that the news would somehow compromise the Fifth House itself, bringing strife to a typically peaceful society. But Grandpa Jace apparently knew members of the Fifth House, and had one of them, Ambassador Lwaxana Troi, intervene. Ambassador Troi endorsed Grandpa Jace's plan to have me undergo surgery. But there was a caveat: My family and I were to remain on Earth until I had matured enough that the average Betazoid, without any aforehand knowledge of my past, would not know I was transsexual. I'm honestly not sure whether I cried harder than my parents, but in the end it was a sacrifice I had to make.
I was renamed Kestra, a name suggested by Ambassador Troi, after her departed daughter. She once told me her daughter had been guided by the Fates to be reborn as me, so similar was my personality to her daughter's. In honor of her help, and as a reflection of my destiny on Earth, I took on her first name as my middle name. I had a fairly conventional girlhood after that, only slightly complicated by my resistance to courtship by boys. I continued to spend as much time as I could spare with my Grandpa Jace, reading his library, especially his "thought experiments for the human condition," and as a side-effect, developing my interest in sociology and in space exploration. It was inevitable, then, that I'd enlist in Starfleet. But I credit my beloved parents, Ashiel and Tommatiel Litalto, my grandfather, Jace McPhearson, and of course the Daughter of the Fifth House, Ambassador Troi, for giving me what I needed to make it this far. I thank my mentor, Admiral Riker, for helping me through his Human insight on Betazoids. I thank my instructors, who were as patient and gentle yet as strict as my own parents. And, not least of all, I thank you, my classmates, for inspiring me to push myself towards excellence, for being my friends, and I hope, for being there with me in the future as we all boldly go where no one has gone before. Thank you.