The legality of buying a katana depends on the jurisdiction and the specific laws of the country or region in which you reside. In many countries, including the United States, United Kingdom, Canada, and Australia, it is generally legal to purchase a katana as long as it is for decorative or martial arts training purposes.

However, it's important to note that laws regarding sword ownership and possession can vary significantly. Some countries have stricter regulations on the purchase, possession, and transportation of swords, especially those classified as "functional" or "live-bladed" swords. These regulations may require licenses, permits, or adherence to specific restrictions.

It is crucial to research and familiarize yourself with the laws and regulations regarding sword ownership in your specific country, state, or locality before purchasing a katana. Consult local authorities or legal professionals to ensure compliance with the applicable laws and regulations.

Furthermore, it's important to exercise caution and responsible ownership when purchasing and handling swords. Always prioritize safety and use them responsibly and within the confines of the law and any relevant regulations.