Technically it’s a girl. Let’s call her FS for now, as in FateSona. She has no problem with her gender but prefers to be as neutral as possible, both in speech and looks. After becoming the Master she asks to call her Master instead of name.It's a first female placeholder I’ve created since school, have mercy on me, my pain is almost physical. Her reason to wear male uniforms has nothing to do with desire to appear/become male.
1) FS isn’t good at handling cold, so she arrived covered in layers of warm clothes. The “Michelin” nickname stuck (sadly, most of the staff that used it got killed in the explosion). Can you imagine how eager she was to enter the First Lostbelt?...
2) FS had always liked uniforms, but not the Chaldea’s ones. Not like she has a taste for fashion, but totally has a style she has zero willingness to betray.
3) Being actually a failing master candidate, FS was salvaged by Chaldea Organisation as the medical team assistant. Capability to adjust mystic codes to improve certain flaws in personal circuits secured a place in a frontline of the backline, involving working with masters directly.
4) There are some tricks to mystic codes attuning. You can't simply take a full body suit and turn it into a bikini with dildo, Gudako!
The same amount of functionality can be spread over the bigger amount of cloth, not the other way around. Color and texture also seem to matter: if FS wishes to get rid of blue ribbon, for example, she has to add some blue embellishments or even bigger elements to the design.
5) Romani Archaman is actually her boss. FOREVER IN HER HEART T_T FS met Mashu, Fou, and the actual Master briefly after actual master and Mashu had met for the first time.
She got better acquainted with Mashu during FS’s medical service, but not too much.
The reason FS ran into the explosion wasn’t exactly Mashu. 48th Master was her significant other.
I really need to come up with a name at this point...