It's about a Tokyo schoolgirl who travels to a world so chauvinistic that her job choices are: (a) slave, or (b) prostitute. She chooses the latter.

This is actually a manga adaptation of a web novel, adapted by the original writer. There's a web novel site (Shousetsuka ni Narou) that's been responsible for lots of recent anime. It has two adult-only child sites: Nocturne (for men) and Moonlight (for women). This novel was posted on Moonlight, but written as a comment on the male sex fantasies on Nocturne. Its starting point was "How would a woman feel, being transplanted into a fantasy world that's shallowly structured around male desires?"

I can't do better than quote the author's afterword.

Now, volume two. Haru's story is currently in the middle stages and a special someone has been introduced who will affect her from here on in. While this story is set in a so-called "other world", the main stage is the Blue Cat Nocturne. Life in another world is like a school festival to JK Haru: every day is so strenuous that she doesn't have time to think about anything else.

The final kick to the can is the trigger that expands Haru's view of the world. To follow someone she's interested in, she goes down a different path from her classmate, gets caught in the rain and experiences a profound her emotion when she looks up into the clear sky. While it's incredibly cliched, this will deepen her world.

In volume three, she will encounter both her first love in her new world and the harsh reality of life there. To Haru, whose perspective has started to broaden a little, this is where her true fight begins. She chooses positive and fun ways to confront her unrelenting reality because she knows it empowers her. That's basically the only weapon she has.

However, it's a cruel world. The people are neither enemies nor friends, but I'm sure you readers also know and have been hurt by coldhearted people. Haru is in that time of her life right now. She's about to get hurt a lot. There will also be many people against whom her strengths won't work. Even so, I'd be happy if you continue watching over her as she becomes optimistic, direct and starts growing into herself as she continues living in another world.

It's realistic. Haru is upbeat, determined and down-to-earth, but the sex scenes are never sexy or even pleasant. It's hard work. Sometimes it's dangerous. One customer nearly chokes her to death... and then afterwards she goes downstairs again to smile and tout for the next one. (She works at a brothel-pub, so she's also a waitress and occasional backing dancer. In this world, men will have a meal and a drink before buying a prostitute.)

"The hair again? I hate this. I might actually go bald from this. The men in this world really love to rape. I get thrown around like a toy in this way about two to three times a night."

We see other aspects of Haru's life. She bonds with her colleagues and has girl chats. She's certainly no innocent, e.g. she worked as an escort back in middle school and declines job offers that would let her leave her current profession. (She thinks they're a downgrade.) She gets excited on seeing a rich potential customer and has set herself the goal of becoming one of her brothel's top three sales.

There's commentary on isekai in general, although this world's prejudice against women is far worse than in most mainstream isekai. To compare with real world examples, though, Afghanistan bars women from non-primary education, from a wide range of public spaces and even from travelling more than short distances without a male family chaperone. They have extreme difficulty getting even basic medical care. Thus, a lot of this manga's worldbuilding is actually real. There really have been instances of what it's portraying.

"It's improper for a woman to go out to eat by herself. You should only do that when you're being accompanied by a man."

"My parents sold me. I have two older sisters, after all. It's something that happens all the time here."

There are also isekai tropes. Haru arrived here with a pathetic nerd classmate, Chiba... but he's male, so he was given amazing cheat superpowers and after six months is already a famous adventurer. Haru made him one of her regular customers and occasionally gives him freebies. She considers becoming an adventurer herself, but only men can register with a guild. There's an exception to that (priestesses with white healing magic, but even they can't register without a designated male partner. We meet a priestess who has all the wrong ideas about Chiba and would love to team up with him. Haru meets up with this girl, has an informative discussion and doesn't tell her the disillusioning truth.

This series isn't depressing (so far), but calling it "fun" wouldn't be right either. Sometimes it's shocking. Haru's customers include horrifying jerks, e.g. the bloke who orders her to fellate him in the public dining area in front of everyone, then gets violent. It's also not sexy, with the artist not even drawing nipples. However, Haru herself is tough as nails and getting on with life pretty well. She's a survivor. She doesn't like her job, but she likes earning money and not being a slave. She's made friends among her colleagues and she's not letting her work define her, instead living each day to the maximum. It's genuinely quite an interesting series.