Ginger Crème Brûlée: a gender headcanon (gender identity, gender presentation, butch/femme, gender feels, etc).
(Another fairly lengthy multi-character answer incoming! Also, as a foreword, while I’ve tried to educate myself and be respectful, I feel that my understanding of genders might be a bit fuzzy at times; therefore I’m always willing to discuss these headcanons and change anything which could seem offensive/awkward.)
Haldswys is trans woman and has admired tough women, heroines and female adventurers ever since she was young. In her restless adolescence years, she dreamed of joining the Sanguine Sirens, but it took her a few years to realize why she felt so drawn to the Sirens in particular.
Although her choice of profession means that she can’t be afraid of getting her hands (or the rest of herself) dirty, she still tends to use makeup and style her hair daily, and she often also paints her nails - even if she’ll have to redo the paint the following day. It makes fer feel better and is part of her gender presentation.
Lumien is cisgender male. Even though he is quite soft-spoken and may have interests which at least in some cultures would be considered feminine, nobody has ever really questioned his identity, himself included. Being tall and somewhat handsome might help, and he knows how to dress well.
Merces’s gender identity is... a bit interesting, probably. For quite a while after he left Azys Lla, he would have probably described himself as agender if someone had asked - but mostly because having a gender felt like something reserved to those who actually counted as people.
Even nowadays, he considers the fact that he is male similar to the fact that he is right-handed or that he is six fulms and one ilm tall: it might affect his physical abilities to a degree, but it doesn’t really mean anything beyond that. He sees no need to emphasize or deny it.
Cain and Brenda are both characters who would rather not talk about their gender because it’s a bit Complicated(TM) and they struggle to make sense to it. The difference between them is that Cain defaults to he/him pronouns and probably identifies at least a little with his birth gender whereas Brenda uses they/them and is nonbinary.
Brenda might also be more likely to correct someone for using the wrong pronoun or moniker (at least if they don’t fear getting ridiculed for doing so); Cain would either not bother or think that the mistake was intentional, roll his eyes and ignore it.