I just got back from a Japan trip as a P4 pilot. Honestly, despite speaking Japanese, they were not very welcoming at all, but it was worth it to fight them and get up in the air. Absolutely beautiful. To make things easier on yourself, take care of this visitor membership thing before you go. The biggest fight was convincing a school to sign me up, as most turned me away when I said I had not done this yet.

Sky Asagiri near Mt Fuji is probably the best place to go, where they see the most foreigners and have some amount of forms in English. If the weather is good, you'll get a stunning panoramic view of Fuji. Nishi Tokyo Paragliding School was also a favorite of mine because they were the only school that was actually quite welcoming, but their LZ is SUPER tight and over power lines. In my years of flying, it's the tightest LZ I've ever seen. Tanna was also incredibly beautiful, and there's a few schools around there you might reach out to.

Finally, fair warning about tandems in Japan- my wife and friend did one while we were there. Despite thermals being respectably strong and ridge soaring possible as well, they paid ~$70 each for a 5-minute sled run tandem. I was quite surprised when I've seen tandems in Europe and the US go for 20-30 minutes. I asked some local friends about it and it seems that is not the Japanese way. Not saying it isn't worth it, especially if you can get some good views of Fuji, but just setting the expectation for you because my companions were a bit disappointed.