Samurai swords, commonly known as katana, are not inherently illegal in Japan. However, their possession and sale are subject to strict regulations and require appropriate permits and licenses.

In Japan, katana and other traditional Japanese swords are considered cultural artifacts and are protected by law due to their historical and cultural significance. To legally possess a samurai sword in Japan, individuals, including both Japanese citizens and foreigners, must adhere to specific procedures and obtain the necessary permits.

The key steps involved in legally owning a samurai sword in Japan typically include:

1. Obtaining a sword possession permit (To-ken Menkyo or To-ken Tōroku): This permit is required to possess a sword legally in Japan. It can be obtained through a licensed dealer or directly from the Japanese government authorities.
2. Meeting certain requirements: The requirements for owning a sword, such as age restrictions, may vary depending on the prefecture within Japan. It is essential 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 samurai 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 important to note that there may be additional regulations for swords classified as Important Cultural Properties or National Treasures due to their 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 samurai sword legally in Japan, it is recommended to consult with Japanese government authorities or licensed dealers specializing in the sale of swords. They can provide accurate and up-to-date information based on your specific circumstances and location.