The katana, or "katana blade" in some contexts within the series, is a common weapon of characters within the franchise. The katana is most often mistaken for Leonardo's weapon, ninjaken
The katana (刀) initially was a word describing any sort of a single-edged sword, Japanese or otherwise. However, in modern day, it is used to refer to a specific curved sword carried by samurai in a set known as the daisho.
Most of the swords deemed "katana" within TMNT media are not curved, and more closely resemble the Ninjaken, a straight sword of ambiguous origin said to be the sword of choice for ninja. Karai has also wielded a katana in the 2007 film and the TMNT mash-up.