You need a Japanese Sony account, Japanese form of transactional currency, and a Japanese address. You do get a 10% new member discount if you can somehow fulfill those requirements, though!
As others have mentioned, proxy service is probably the cleanest way if you're not in Nippon. Otherwise you can try retailers like "nin-nin-game" who have both the Walkman and headphones up for sale (take their terrible reviews with a grain of salt, I got my JP KH3 PS4 Pro from them fwiw).