My instructor and the students of his who went on to teach, myself included, have always addressed students formally in the dojo as "Mr. [last name]" or "Ms. [last name]." I briefly had a transgender student. He identified as male, so I could use Mr. with him. But I know that increasingly people feel more comfortable with or adamant about neither/nor both/and identities, and that got me thinking.
I really don't want to use first names (too informal) or just last names (too disrespectful). But I don't want to use Mr. or Ms. if that disrespects someone who doesn't identify as such. I was thinking about using sempai, but don't think that fits, as I believe we reserve that term for the senior kyu grade student. Then again, I don't speak Japanese, so maybe I'm wrong about that.
Does anyone use formal, sex-neutral honorifics when addressing students? What are they?