all sets : https://e-hentai.org/g/4059774/57be676178/
fanbox : https://www.fanbox.cc/@rena-bootleg/
https://www.pixiv.net/en/users/117328254

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

The title gives even more context: いじめ_文字あり > Bullying, with added text/sfx.

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.

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]
the title shows: いじめ_文字あり [ijime _ moji ari = bullying - with added text

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."
--

Base +26