What an interesting lore background there. There's a big chance that this is a post apocalyptic setting where old humans became a lost civilization of some sort. The fact that the language settings has old languages might clue that this is a future version of his own world and not an alternate world.
I'd love if the author would delve more into the whole past and war as that lore tidbit just made things a lot more interesting. Also I'm really curious if we'll meet her trash sister there at some point lol. Maybe she's the protagonist character of the otome game lol.
fuck. i'm re-reading this again just to kill boredom and holy shit after reading God's Activity in a World Without Gods, it just occurred to me that there might have been an dimensional invasion in the future and this world is probably the future of earth and not another world lmao. if you think about it, it makes so much sense now. at least for me lol
Rice, Soy, Miso, Onsen.
The four cornerstones without which Nippon-jin cannot survive isekai. They just absolutely fucking die if they can't have these things.