Lots of fun things to do in Japan. I’d just get out and try new things, visit places, eat all sorts of food, and immerse yourself. Ride trains, ride bikes, visit shrines and temples, see the fall colors in the autumn, see the cherry blossoms in the spring. With a bike and train pass you could see most of the country, no joke. I’d catch local festivals too.

If you’re a member of the Church then consider getting involved in thr local ward/branch. They need help. Most buildings will probably have free English classes taught by the missionaries weekly. Maybe help out there too to make friends and serve.

Japan has all sorts of varying climates from beaches to temperate areas to mountains and dormant volcanoes.