Vax'ildan was accustomed to disrespect.
Living under Syldor's rule, he and his sister were looked down upon, called "half-breeds" when people thought they weren't around. When they had first arrived, his sister helped him to appear as masculine as possible, had assured him that the name "Vax" was perfect.
And, yet, as soon as Syldor saw them he demanded that Vax change into something "more ladylike," so as not to embarrass him. He referred to Vax by his birth name, and often spoke less-than-lovingly about his two twin daughters.
Vax hated it.
In the spirit of petty revenge and teenage rebellion, he slept around with members of Syldor's royal guard, and made sure that rumors spread. His sister thought he was being childish, but he just thought he was making the most of a bad situation.
When they had finally had enough, when he had finally had enough, they left, and spent the next few years wandering from city to city.
Finally Vax was free to wear masculine clothes and armor, free to wear his hair in the style of men rather than women, free to call himself by his chosen name, his real name.
Still, not everyone respected those wishes. As his breasts grew and became harder to successfully bind, as his waist and hips became curvier, and as his facial features bordered the line between masculine and feminine, he would sometimes be mistaken for a woman. Whether it was a barmaid, a shopkeep, or someone he elected to spend the night with, people would invariably mistake him for a woman.
Sometimes, when he corrected them, they apologized, confused. Other times, their eyes would take on a malicious glint, understanding the situation perfectly, and would make every effort to misgender him. Usually, that was when he and Vex would leave a town, when rumors of half-elven twins, two girls except, did you hear?, one disguises herself as a man. One refuses to tell anyone her real name, gets angry if you let her know that you've figured out her secret.
Vax hated it. He hated the disrespect he suffered at the hands of these nobodies.
Over time, he became better at managing his appearance. His deeper voice felt more natural than what had been his regular voice, and he was able to fit into men's clothing correctly. He and his sister saved up until they had the funds to go to a cleric and request that they fix his chest problem. And it was done, no questions asked, and Vax had never been more relieved than when he finally threw away his old binding materials, and began buying smaller shirts to account for his flatter chest.
Most importantly, people stopped mistaking him for a woman.
The exception was some of the people he slept with. It's not that he was the type to need someone in bed with him every night, but every now and then it was nice to have that sort of comfort. Unfortunately, when he and his partner for the night would retire to some room at an inn, and he would explain his… situation… downstairs, not everyone reacted kindly.
Some accused him of tricking them, some were just disgusted by his anatomy, and some didn't attack or accuse him, but made excuses for why they couldn't spend the night with him. Not everyone was so hurtful, but plenty of them were, and over time Vax grew used to the disrespect, began feeling as though he should apologize every time he got undressed.
When he and his sister joined the group of people who would become Vox Machina, he was scared to lose this group of people. They had found someplace they could feel like they belonged, and, the longer they traveled and fought with this group, the more important the people in it became to him.
When they eventually, inevitably, found themselves camping near enough a river and with enough time that they had the chance to bathe, it was expected for all the men to bathe at once, and then all the women.
Vax was terrified. He knew them to all be good people—er, well, decent people who were friendly to the twins and whose interests aligned with their own—but he had been sure that some of his previous bedfellows were "good people," until they turned on him once his pants dropped.
He wasn't worried that any of the men who would see him would become hostile, but he was sure that at least some of them would treat him differently.
As he and the other men passed the women on their way to the river, Vax and Vex shared a worried glance.
However, when they all disrobed, Scanlan and Grog making jokes, as always, Vax did not get the reaction he was expecting at all. In fact, he got almost no reaction. Scanlan make a lewd joke, Percy had the decency to look embarrassed, and that was that. As they all moved into the chilly water of the river and began scrubbing the grime away, nobody made a big deal of it, of him.
It took everything Vax had to not start crying tears of joy and relief. He had worked himself up, anxiety turning his stomach, ready for the worst-case scenario, and now all that bottled up energy tried to escape. Rather than breaking down sobbing, he did the first thing he could think of, and splashed Grog.
Of course, he blamed it on Scanlan, and when the goliath went to splash the gnome back, his large and powerful arms created a wave large enough to soak just about everyone, and, soon enough, they were having a miniature war, laughing their asses off.
And if some of the water running down Vax's face wasn't from the river, well, no one mentioned it.
Maybe there were some decent people to be found.
