@RUD3DUD3
plus how the fuck did someone like him would even know that manga? didn't the girl say the manga is passed down in the family generations after generations? i was expecting iruma to be completely oblivious to the manga given the life he had lived in human as a slave that is.
The hilarious part is it's even suggested that he worked as a mangaka assistant. I hope it wasn't trying to insinuate that he worked on THAT very manga, but it wasn't clear.
As for how... Well... It is a different dimension or plane of existence and the contact between humans and demons is so rare that most think humans are a fairy tale. So it could be that time just works differently there and generations have come and gone while only a decade or two has passed in our own. Kinda curious how her family got such a manga collection in the first place, however.
Then again, it could be a "Rose of Versailles" type situation where the manga is actually older than him but it was so popular that even newer generations know about it. I mean, I'm not even Japanese nor was I born prior to 1972 and even I know about that manga.