I frankly just think this manga is an exercise of absurdity. It's as if the artist wanted to make a shocking story as a way of getting attention, landing on making the story an NTR isekai, but didn't actually wanna make real NTR cause it's weird and gross. So instead we have this weird, whitewashed idea of NTR; Naoto is fucking girls that Shinji likes, but isn't like, really involved with, guys, so it's not like Naoto is really doing something that would ruin a friendship and breed hatred and contempt. And, of course, he's doing it as a way of "helping" his friend, so it's not like he's really doing something bad and self-serving, guys. It's just ridiculous. The NTR shouldn't be in this story.
The story dynamic, I feel, would actually be fine, great even, if not for the addition of NTR. I love the dynamic between two friends, where one is generally jaded and cocky, and one is trusting and friendly; think Hans Solo and Luke Skywalker. Not quite a student and a mentor, but more so two friends who end up teaching each other about the world, due to their different personalities giving them different perspectives on the same issues; the differing perspectives of the friends clash and meld and they both learn more than they would have by themselves. This wonderful dynamic then gets sullied, really outright ruined, by the fact that, well, one of the two friends is doing something that fucks up the friendship and the whole mood of the story. This actually happens fairly often in NTR stories, especially when they're longer than a single doujin. A few NTR stories have the one getting NTR'd have a fairly friendly relationship with the one doing the NTR, and it's always somewhat sad and annoying as a reader.
Have these mangaka never had friends? It's not the kind of thing you do to a friend, if you have any human dignity. I think I would sooner kill myself than willingly sully my friend's relationship with his partner in any way, unless that person was actually toxic and abusive in some way; in that case, though, I would probably just kill the bitch, not fuck her. Even if I had a mystical ability to fuck bitches to death, I wouldn't use it as a matter of basic manly honor, I'd snap her neck or something. It seems to me that any author that would write this kind of story simply must either have no idea of or interest in manly honor, as I can see no other way that anyone who is kind and honorable towards the ones that they would be friendly with could even consider making a story like this and think it's good. Maybe if the blonde ikemen character just drained the female characters, it would be fine, but introducing the sexual aspect, making the story NTR, just ruins it and makes it a weird and distasteful work.
Really, I think that's the main point to be made: The story would be fine, but the NTR ruins it wholly, not just from its presence alone, but also the execution of it. I would love to see these two friends journey through a fantasy world, make friends, make enemies, clash and make up. The fact that one of them is NTRing his buddy just fucks it up and gives me a bad taste in my mouth. What makes it even worse is that it's such cowardly NTR too, frankly. "Bro, it just so happens that all the women that Kenji likes romantically are also trying to like, deceive him and take advantage of him and stuff, so of course Naoto is gonna fuck them to protect his bro." It's as if the mangaka is afraid to actually make it real NTR, or maybe just unwilling to. Probably the latter, honestly. Without the NTR, if you can even call it that, this whole work is just a generic isekai in the generic setting common to isekai, but with an interesting character dynamic, with the aformentioned two friends with wildly different personalities and worldviews. Of course, that's probably hard to sell, or at least just as difficult to sell as any other generic isekai with only one or two notable aspects that set it apart from other generic isekai. So, we get this instead: A work trying to do something shocking, cynically hoping to get more attention than it rightfully would get, without the actual guts or passion to make it all that shocking or interesting.
This story would be leagues better with a Rance type of guy going around and actually fucking a bunch of dudes' actual wives, if the NTR is so essential. Hell, keep the NTR, just don't have one of our co-protagonists doing it to the other; imagine two guys, one is a total troublemaker, a hardcore Rance type, the other guy is just kinda quiet, demure, and mostly quiet, but goes along with the troublemaker all the time. The two have been together since childhood, the troublemaker always finding some new, fun way to make some trouble, and the quiet friend goes along with it and they both have a bunch of fun. The troublemaker friend gets a good idea one day when they're just about adults and around that adventurer age: "Bro, let's go on an adventure and fuck married women all around the world." Then the two depart, and do exactly that. Hell, they go so far, fucking so many mens' wives, that they end up making it all the way to the Demon King, the big bad, the ultimate evil. What do they do? Fuck his wife. Boom, story ends. Better than this weird story where we have a guy fucking all of the women that his friend is interested in, in some weird, stupid way of "protecting" him from all these women who have to artificially have ulterior motives to justify the NTR shit, I'd say.
tl;dr I dislike the NTR in this manga. It's not the NTR, it's how the NTR is done. It's weird, distasteful, and annoying that Naoto is fucking women that Shinji is interested in cause they for some reason all have ulterior motives and are trying to take advantage of him, and Naoto simply needs to fuck them to stop them. It's fake NTR, trying to use the name of NTR for the shock value and clickbait, and then trying to whitewash it to make it palatable for normal people. If not for the fake NTR, or if it were real NTR but without the protagonist doing it to his friend, this manga would be pretty damn good, I think.
