Katana is a type of Japanese sword , often referred to as a Samurai Sword. The term is sometimes incorrectly used as a generic name for Japanese swords. The katana gets its gentle curve from quenching during forming; it is actually straight prior to quenching. Differential quenching causes martensite to form predominantly in the edge of the blade rather than the back; as the edge expands, the blade takes on a gently curved shape. They were the main weapons of the Samurai.