The legality of using a katana, or any other type of weapon, for self-defense purposes depends on the specific laws and regulations of the jurisdiction you are in. Self-defense laws vary widely from country to country and even within different states or regions.

In many places, the use of deadly force, including the use of a weapon like a katana, is heavily regulated and generally only justified in situations where there is an immediate and credible threat of serious bodily harm or death. The use of any weapon for self-defense is typically subject to the principle of proportionality, which means that the level of force used must be reasonable and necessary to counteract the threat.

It's important to familiarize yourself with the laws and regulations regarding self-defense and the possession or use of weapons in your specific area. Consulting local law enforcement or legal professionals can provide you with the most accurate and up-to-date information regarding the legality of using a katana or any other weapon for self-defense purposes.

Remember, responsible and legal self-defense typically involves seeking non-lethal options, such as personal alarms, pepper spray, or engaging in self-defense training that focuses on techniques for disengaging from dangerous situations and escaping harm.