While it is not entirely accurate to say that it is illegal to own a sword in Japan, there are regulations in place regarding the possession and sale of certain types of swords. These regulations are primarily governed by the Japanese Sword and Firearms Control Law (known as the "Sword Law"), enacted in 1958 and amended in 2019.

The Sword Law was put in place to control the possession and circulation of traditional Japanese swords, particularly those classified as Nihonto. Nihonto refers to swords made in Japan using traditional methods and are considered cultural artifacts with historical and artistic value. The law aims to protect the integrity of Nihonto and prevent their illegal trade and export.

Under the Sword Law, individuals in Japan are required to obtain certification, known as a "sword license," to legally possess and trade Nihonto. 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.

The regulations also extend to non-Japanese residents who wish to bring a sword out of the country. Exporting Nihonto from Japan requires appropriate permits and compliance with export control laws to prevent the unauthorized removal of cultural artifacts.

It's important to note that these regulations primarily apply 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.

Overall, the regulations regarding swords in Japan aim to preserve and protect the cultural heritage associated with traditional Japanese swords while preventing their unauthorized trade or export.