Katanas, which are traditional Japanese swords typically characterized by their curved blade, are regulated in Japan. The possession and sale of katanas are subject to strict regulations under the Sword and Firearms Control Law (刀砲刀剣類所持等取締法, Tōhō Tōkenrui Shoji-tō Torishimari Hō).

In Japan, the possession of certain types of swords, including katanas, is allowed, but it requires appropriate licensing and registration. The law categorizes swords based on their historical or cultural significance. Genuine antique swords that hold historical value, such as those recognized as Important Cultural Properties or National Treasures, are generally allowed for possession and sale.

However, the possession of non-traditional swords, replica swords, or modern-made swords without significant historical value may be restricted or prohibited under the law. It's important to note that the specific regulations can vary depending on the type of sword, its age, and other factors.

To ensure compliance with the regulations and to acquire a katana legally in Japan, it is advisable to consult with Japanese government authorities, such as the local police or the Agency for Cultural Affairs. They can provide accurate and up-to-date information on the possession and sale of katanas, as well as the necessary procedures and permits required.