After some more research from the artist, you can find that she draws lots of otokonoko [males wearing dress/crossdressing] and being bullied. So, this is consistent.
Now I'm pretty sure that it's a boy as implied in the character conversation and reaction: More or less like this: please correct me but the meaning is at least has similar vibe [I remember now, it's koufun not kyoumi]
There's the ドM-> means super masochist .[on the table writing]
Onna no ko no mizugi o kisaserarete, kōfun shiten'no? Kimō w. 女の子の水着を着させられて、興奮してんの?キモーw Translation:
"Being forced to wear a girl's swimsuit... Are you getting excited by that? Gross, lol." or "Made to wear a girls' swimsuit, and you're getting turned on? That's creepy, lol." --
If the character is consistent across the gallery from beginning to the end, then this gallery is all about a male character crossdressing as a girl and found out then being bullied and 'bdsm'ed/bondaged by the girls.
1 - 20 - is a questionable female. It can be a male crossdressing too [ look at visible bulge on the crotch area too] 141 - 176 - visible bulge on his crotch 177 - 232 - visible bulge + balls on his crotch.
This gallery is a boy [tomgirl] crossdressing as a female. look at the body shape too Another one [the other character is possibly a girl, but not sure since everything is covered up], but the real evidence is the bulge on the crotch and balls-like shape