Following a long line of fantasy meets modern day stories, this Isekai series throws student dropout Suzuki Touru into a world of danger when he rents a super-cheap apartment that contains a doorway to a dungeon. Daring to enter, he finds a young Knight named Aria Eldrax (or Ria for short) suffering the after-effects of a poison dart. Bringing her back to his room, he embraces his percieved role as a mage and begins to explore his newfound reality.
The first setup like this I encountered was back in the 90's with Ah! My Goddess - an everyday loser suddenly blessed with a young, naive beauty to lust over. Back then the series was balanced by Belldandy's bratty younger sister, Skuld, and worldly-wise older sister Urd. Reading this, I can see why that balance was sorely needed.
This is a fairly standard male fantasy trope, coming to the aid of a vulnerable young maiden and discovering love (or lust), but you need something to act as an impedement to overcome so that both of the leads can grow appropriately. This feels like an abduction.
Touru lies, hides his porn and plays the part of a respectable figure, all under the guise of making his newfound babe-in-the-woods understand the world she's found herself in. Ria is naive to the point of alarm, as she's not only believing everything she's told by this lying little sod, but allowing herself to be dressed by him, washing his underwear and volunteering to share a bed. It would have been a great twist to see her wink at the reader to suggest she's putting on a show to snare the lustful idiot, but no, she really is that submissive. It's alarming and I want to have a strong word with her parents about stranger danger.
If you want to go all in for a male fantasy of this nature, you either give your lead some redeeming qualities (Tenchi would at least stand and fight, and had the sympathetic part of being tossed around by chaotic winds) or you go full tilt and write Saki The Succubus Hungers Tonight, a book that acknowledges it's cheesecake intentions by drawing shocked faces on the main character's willy and making it talk. I mean, commit or get out, really.
The book isn't without merit. The art is very appealing - attractive designs that wouldn't look out of place in any of the Isekai books doing the rounds. Panel layouts are excellent with some dynamic scenes and suitably angled fanservice to please the intended audience, but despite Ria's stated age being 18, she only looks it when naked. I certainly wouldn't carry it with me on one of my Korean business trips as it would absolutely fall foul of the laws introduced there for depictions of underage sex.
In terms of the story, when it isn't being creepy it has moments of wit, though falls flat when aiming for warmth or sweetness as it's hard not to remember what Touru's doing to get to those places. Ria mistaking Touro's anime figures for magical talismans is quite amusing, and marking his porn as "Forbidden Magical Tomes" is as good a way as any of keeping his stash safe.
In true genre fashion, there are slimes, RPG stats, other races and rules to the Dungeon world, but beyond a starstruck young lad getting a thrill with a girl way out of his league, it's just not much to write home about.
I don't hate the book, I just don't like the protagonist (or antagonist depending on your viewpoint). There's just too much in the way of superior competition to make this anything more than an "also ran". Before you get to this, I'd recommend Rising of the Shield Hero (it has layers and themes whatever you may think of them) or That Time I Was Reincarnated as a Slime, wherein our hero Rimuru shows genuine political nounce, guile and empathy in his newfound world. Not to mention a clever counter-narrative at the back of each book that puts events the reader has witnissed in a new light.
If you like Dungeon Rest-Stop, that's fine. It'll have it's fans and that's not a problem. But you could be reading something better in the same genre, so maybe cast around a little and see what else is out there. This is not the genre tentpole you are looking for.