“Basically…” Making a face like she was fending off a headache, Togame answered Shichika – without turning around, eyes fixed on Kiki Shikizaki. “He means the Twelve Possessed – were manufactured using methods of the future.”
Zento the Leveler. Zanto the Razor.
Sento the Legion. Hakuto the Whisper.
Zokuto the Armor. Soto the Twin.
Akuto the Eel. Bito the Sundial.
Oto the Cured. Seito the Garland.
Dokuto the Basilisk. Ento the Bead.
“Whoa – not just the Twelve Possessed. All thousand of the Mutant Blades – were manufactured using methods reimported from the future, which I divined.”
“From the future? Reimported?”
“Get it?” Togame said, out of patience. “That’s why to us, living in the present day – they seem to possess characteristics that defy the laws of physics.”
So hard that it could never bend or break. Sharp enough to cut through anything.
Complete and utter uniformity. Tuned to be as light and frail as possible.
Ironclad and matchless armor class. The heaviest matter in existence.
The power to revivify the body. A robot almost perpetually in motion.
Precise alignment of the spirit. An ability to gauge sincerity.
Impregnated with ferocious venom.
Each and every one – had characteristics unimaginable in a regular sword.
But their unimaginable nature was strictly limited to the present age.
Who was to say they would not become regular in the years ahead – hence!
Nothing stops you in the present, if it can be done in the future!
Reimportation!

Katanagatari Omnibus 4, Page 195