Swords are not illegal in Japan, but their possession and sale are subject to strict regulations due to their cultural and historical significance. Traditional Japanese swords, such as katana, fall under the category of "Nihonto" and are recognized as important cultural artifacts.

In order to own a sword legally in Japan, including katana, individuals, both Japanese citizens and foreigners, must adhere to certain procedures and obtain the necessary permits. These procedures typically involve:

1. Acquiring a sword possession permit (To-ken Menkyo or To-ken Tōroku): This permit is required to legally possess a sword in Japan. It can be obtained through a licensed dealer or directly from the Japanese government authorities.
2. Meeting specific requirements: The requirements for owning a sword, including age restrictions, may vary depending on the prefecture within Japan. It is important to consult with local authorities to understand the specific regulations in the area where the sword is being acquired.
3. Purchasing from licensed dealers: It is advisable to buy swords from authorized dealers who are knowledgeable about the legal procedures and can guide you through the process. They can assist with obtaining the necessary permits and ensuring compliance with the regulations.

It's worth noting that there may be additional regulations for swords classified as Important Cultural Properties or National Treasures, as they hold higher cultural and historical significance. Exporting swords out of Japan may also require appropriate documentation and permissions.

To ensure compliance with the regulations and to acquire a sword legally in Japan, it is recommended to consult with Japanese government authorities or licensed dealers who specialize in the sale of swords. They can provide accurate and up-to-date information based on your specific circumstances and location.