Yes, and the reason people ask is worth unpacking.

Japan does not filter the internet the way some countries do. There is no national firewall and no government blocklist standing between you and the web. What stops you is almost always commercial geo-locking: a Japanese service that holds rights for Japan only and turns away every foreign address, or a global service that shows a different catalogue in each country. Using a VPN to change which side of that line you are on is legal in Japan, and so is using one for privacy.

There is one rule worth knowing, because it catches people out. On 1 January 2021 Japan's amended Copyright Act made it a criminal offence to knowingly download pirated manga, magazines and academic texts, extending a 2012 law that had covered film and music. The maximum penalty is two years in prison or a fine of up to two million yen. Officials involved in the law have said enforcement targets repeated and deliberate downloading following a rightsholder complaint, rather than someone who clicked one bad link. Either way, the point stands: a VPN changes what your provider can see, it does not change what is legal. Stay with the licensed services and this never becomes your problem.

What a VPN does in Japan is more ordinary and more useful. It encrypts your connection on the open Wi-Fi at stations, airports and convenience stores, and it lets you choose which country's version of the internet you are looking at.