Katana means cutting edge up, Its a single edged traditional japanese swords mostly used by ancient japanese samurais, you might have seen similar one used by one of the ninja turtles. It requires a great craftsmanship to create one, From traditionally smelting of iron to forging to polishing is no easy job needs a great expertise, which make it the best sword in the word and more superior than the other. A trained katana warrior can cut a man into two with just a single blow which is possible because of both strength and sharpness of the sword. Nothing other than the below video can explain How Katana Sword Is Made and the science behind it. Its quiet a long one but i am sure it will amuse you.