Tie a squid to a knife and you get a sword! Knives are too small to be considered a sword on their own. That's why you strapped a squid to it. They're the right shape, kinda pointed, so no one will know it's just a knife.
You learned how to make swords this way from Ken (けん) the samurai. He put his own little squid buddy on his knife and now no one realizes it's not a sword!