fwiw there are all kinds of hiking in Japan—one of many places you might find challenging is the Mt Yari / Hotaka area
(easy hikes are also wonderful and good to have)
(easy hikes are also wonderful and good to have)
For much better info on hiking the Japan Alps, Tom Fay’s books and site are a great start.
(I don’t see his Twitter account anymore) https://thomasfay.com/japan-alps-mt-fuji-guidebook/
(I don’t see his Twitter account anymore) https://thomasfay.com/japan-alps-mt-fuji-guidebook/