The legality of possessing a blunt sword, or any type of sword for that matter, depends largely on the laws of the specific jurisdiction in which you are located. Some places may have restrictions or outright bans on the possession of swords and other bladed weapons, whether sharp or blunt, while others may have no such regulations.

As of my knowledge cutoff in September 2021, for instance:

• In the United States, laws about sword possession can vary widely from state to state. Some states have very permissive laws regarding bladed weapons, while others are more restrictive. It's generally legal to own swords in most U.S. states, but carrying them in public can be illegal in certain circumstances.
• In the United Kingdom, it is generally legal to own swords including samurai swords, however, it is illegal to sell, hire, lend, or give anyone the following: butterfly knives (also known as 'balisongs') - this includes trainers; disguised knives - where a blade or sharp point is hidden inside what looks like everyday objects such as a buckle, phone, brush or lipstick; flick knives (also known as 'switchblades' or 'automatic knives') - where the blade is hidden inside the handle and shoots out when a button is pressed; stealth knives, which are knives designed to avoid detection by metal detectors; zombie knives - a knife with a cutting edge, a serrated edge and images or words suggesting it is used for violence; swords, including samurai swords - a curved blade over 50cm (with some exceptions, such as antiques and swords made to traditional methods before 1954).
• In Australia, laws are different between states, but generally, you are allowed to own a sword if it is used for purposes such as display, collection, historical re-enactments, or martial arts training. Carrying a sword in public, however, is generally illegal.
• In Japan, traditionally made swords (nihonto) are considered national treasures, and there are strict laws regarding their production, sale, and export. Non-traditionally made swords, such as those that are mass-produced or made from modern materials, are typically more loosely regulated.