Animosity
im guessing that he reincarnated in the same world just MANY years later after humanity took back control and other scientists found out more about the life equation and discovered the runes that make the universe as the author explained in the comments. and then magic became common place. the only thing missing is why the place is so medieval and not futuristic.if im wrong and he really is in another world then the author needs to explain how humans found out about the runes and how the first mages were born without there being a scientist like seth was and without technology