God damn, this may be the worst take on the "Removing the Crucial Teammate" trope in the history of japan running that trope into the ground. The art is OK, and that doesn't come anywhere near saving an utterly lazy plot with absolutely inane developments. Even leaving your brain at the door and...
Or set the story backwards technologically: bronze was usually cast (though it can also be forged). Though obviously that has the issue that you now need the world systems to make bronze.
Or just the basics. Or asked, I'm sure there are plenty of smiths who'd be happy to help.
Or even just...
It's garbage though, and translated straight it would be just that.
However the translation manages to make it camp, so bad it comes 'round again to being good.
It's not like that means much. "Seinen" just means it's published in a magazine which targets adults. That means they can cover more adult and complex themes than shonen would, but by no means that they have to, and manga can be moved between publishers (e.g. trigun and vinland saga were both...
Well crap I wanted to rate it a 10 because of how good the last few chapters were... but I've already rated it a 10.
Somebody else please rate it a 10 in my stead.
There are other iseka which do it this way, but better ones actually integrate it logically e.g. in the "game world" death is permanent which explains how progress is much slower & there may be various undiscovered things, inhabitants of the world can not take anywhere near the level of risk...