I know you joked that we would be questioning why Nobunaga had weapons like that but we really do have to ask xD.
It can't just be " it's magic bro". My guess is that Nobunaga was also not the original owner. Cause if he is author's got explaining to do. And not sime hand wavy explanation
Does it mean that by the time he got summoned/transferred/transmigrated hundreds of years had already passed? Because how else would the tome of blessing have weapons ahead of his time.
Ahem. The age of consent thing being 18...that's for humans, no? So—Wait! Unhand me!