wait he just said a magic barrier. so does that mean they know what magic is or don't they cause she thought magic was a type of swordsmanship in the last chapter.
By this point the plot seems very obvious, for anyone who want know here are my predictions
The black sun somehow has manifested itself on earth and has replaced magic has as norm to their magic sword system and have turned the humans against (due to lack of magic talent and knowledge passing down) the magic system in hopes that the human themselves will find the last sage AKA the demon king and kill him. Basically kill with a borrowed knife.
Now i could be totally wrong but from the experience of read such manga all signs point to the direction.
Ofc the most generic type of shit would had one, watching from afar, just saying "Interesting", end the chap and became and pain in the ass later date ;-;