Like others have said, they/them is probably your best bet - I'd personally stray away from xe/xem if the character is simply ambiguous or unknown, simply because that might give players the impression that the character themselves identify as non-binary (which can make any potential gender...
I could never think of a situation in which a reply that is less than three sentences is ever an adequate roleplay response. On average, less than three sentences is literally less than fourty-five to sixty words. Replies shorter than that speak to me of nothing but a lack of effort or investment.
A lot of my interests fall into various idol series, but if I had to name the fandom I'd love to RP, it's Megaman. Not a lotof people enjoy it as a fandom, though.