Here's the scenario of the world---its sun is Psi Serpentis Alpha, and its people are somewhat homogenous. They look human on the outside. (Internally there are some differences.) They never had gods, but they have a sort of generalized spirituality involving an Oracle--she is supposed to be eternal, but no one knows if she really is eternal, or is a succession of Oracles. She lives within the sacred mountain Clymaiad (aiad means Mount) above the city of Clymele. And when this part of the story takes place, the world is dying--it's overpolluted, over populated, and generally in bad shape. Eventually, when the main character, who in this part of the story is writing a journal of his past, is in his twenties, an alien arrives from another dimension, and changes the world back to what it had been before the people arose, restoring its beauty. (An aside, the alien is the last of his kind, and what his kind did was to uplift and reform a species, and then rule over them in a benevolent dictatorship. He calls this process Jimat, or formation, in his language.) So the story here takes place at least ten of their years (close to earth years, similar type world in many ways) before Jimat.
Rather than kingdoms and religious wars, the people of this planet are ruled by clans who have armies and hired assassins. Wars that occur (as they do) are fought over money and land. The sexes have equality, but differ in dress and how they wear their hair. Most men and most women wear their hair long--men often braid theirs in three or four braids, clasped at nape and end with cloth or wire. Women wear their hair in single braids or pinned up under scarves, at least in the northern territories. But third gender people by custom have more fluidity in what they can wear and do wear. None of this is law, just custom. Prostitution, also, is an honored guild on their world. They call it comfort work, and comfort houses are a combination of restaurant, hotel, bar and places for comfort workers to meet with clients. So there's no stigma to comfort work, except that those on the bottom rungs of society, pre-Jimat, of any guild, make less coin, and work harder for their living.
Also, most people of this planet are pretty much in the middle of the Kinsey scale, (zero to six, zero being exclusively heterosexual and six exclusively homosexual). No stigma there, either.
The FtM character is identified as Mentesnin, which is a male's name, or Mente for short. Mente was very young when introduced, but half a year later, breasts are beginning to develop, and secondary sexual characteristics. And Mente is interested in the main character's very first lover, who is a male, like the main character. But the lover has chosen to be with the main character, and Mente is jealous and angry and at the same time, attracted to the main character as well. And since he's never been with a woman, his inclination naturally is to treat Mente as a female, because it's his first encounter with anyone trans. Mente doesn't want him on those terms though. So there's some conflict brewing, and I'm still playing it out in my head. I see scenes before I write them...almost like a holographic camera, if that makes sense.
So MY inclination was originally to call Mente "he" and "him" but Mente said no, go ahead and use "she" and "her" but I think that's changing. Maybe as a result of the body changes.
Transition on that world, pre-Jimat, wouldn't be simple as it would be a matter of affording a Healer's help. And I don't know if they had surgical techniques perfected or not. I think they do after Jimat, but not, maybe, before. Balancing hormones, I think they had, but one had to have coin to do it, and as a member of the laboring class, galley help on a ship as Mente and the main character are, it would cost too much, which would lead to a great deal of frustration too.
Eventually the main character mentions that he meets Mente years later and he is living as a male, married to a ruling clan's zunzuh'hru (warrior, soldier). But they don't speak or interact, as the main character by then is a street comfort worker, lowest class of that guild, and working at staying out of trouble, not drawing attention to himself.
So I think I may wind up using a neutral pronoun. My personal inclination is to use whatever a person prefers. I've known guys who dressed as female who nonetheless preferred to be "he" and "him", and those who were pre-transition who preferred "she" and "her." I try to respect and honor that person's choice of gender pronoun preference. Hard, in a language which sorts by twos. (either/or, you know.)
I'm still trying to figure Mente out. But I think Mente is trying to figure Mente out, as well. Awfully young person.
