Katanas are not illegal in Japan. In fact, they hold significant cultural and historical value in Japan as traditional weapons. However, there are regulations in place to control the possession and trade of certain types of swords, including katanas, under the Japanese Sword and Firearms Control Law (Sword Law) I mentioned earlier.

The Sword Law was enacted to regulate the possession and circulation of Japanese swords, particularly those classified as Nihonto. Nihonto refers to swords made in Japan using traditional methods and craftsmanship. The law aims to preserve the integrity of Nihonto as cultural artifacts and prevent their illegal trade or export.

Under the Sword Law, individuals in Japan are required to obtain a certification called a "sword license" (tōken kigen), also known as a "sword possession permit" (tōken shō), to legally possess and trade Nihonto, including katanas. These licenses are issued by the prefectural police and require individuals to meet specific criteria, including age, background checks, and proof of membership in a recognized sword-collecting organization.

However, it is important to note that the Sword Law primarily applies to Nihonto and not to other types of swords or bladed weapons. Other types of swords, such as replicas, decorative swords, or Western-style swords, may have different regulations or no specific restrictions on ownership.

To summarize, while there are regulations in place for the possession and trade of certain types of Japanese swords, including katanas, they are not outright illegal in Japan. The regulations are in place to protect the cultural heritage associated with traditional Japanese swords and prevent their unauthorized trade or export.