The full title of this manga is I'm a Behemoth, An S-Ranked Monster, But Mistaken for a Cat, I Live as an Elf Girl's Pet. You have to admit, this manga is precisely what it says it is on the label.
It is probably the most sexist manga I have read for ages. And that seems to be the entire point.
The story falls into the isekai genre – where characters live in a fantasy Role-Playing Game world complete with User Interface displays for their power stats that only make sense to players of RPGs. The hero, a heroic knight, is killed in battle and finds himself reincarnated as a behemoth with massive destructive power – but in the body of a cute kitten. He gets adopted by a low-level warrior elf girl named Aria, who initially thinks he's just a cute kitten but gradually sees he has powers that can help her in battle. He vows to protect her from ogres, goblins, and lecherous, sexually harassing warriors while enjoying the benefits of sleeping with her, nestling in her ample chest. There's a lot about her chest.
The story began life as a light novel (Japan's designation for Young Adult) by Nozomi Ginyoku that became popular enough to warrant a manga adaptation to gain new readers and, of course, entice fans to buy a visualization of the story. And it is very much For Horny Boys Only. It acts like the Bechdel Test doesn't exist, because the specific target audience – the ecchi (which means 'sexy' in the 'softcore' mode) – are only here for the leering oversexualized female characters and, of course, boobs. Discreetly covered but very prominent boobs. To read what the definition of "ecchi" is to be presented with a checklist of #MeToo nightmares – they go beyond leering poses and exposed boobs to full-on sexual harassment and groping. These books come shrink-wrapped for a reason.
I was sent a review copy by Yen Press and decided to read it as a bit of sociology. It certainly gives us a look at some specific fetishes of certain okatu who buy these books. In Japan, "otaku" are considered nerdy, sexually repressed fanboys who live for their fetishes and fantasies. This series caters to the fantasy of being a kitten so you can hang out and take baths with a hot elf girl with big boobs. Elf girl can fight but is at heart submissive, which is the usual sexist fantasy that shy boys have when they can't talk to girls in real life. It's clear to me that author Ginyoku and artist Taro Shinonome worked closely with his editor to make sure certain moments, beats, and sexualized poses are in the manga. To call a book like this sexist and embarrassing is the same as calling water wet. It does exactly what it sets out to do.