Many foreigners might think that Japan is full of skyscrapers and lack of nature but the truth is different. There are many mountains and well reserved nature throughout Japan.
Therefore trekking is very popular in Japan, especially among seniors and middle age generations. 1 day trekking is common but there are many places where you can enjoy overnight trekking in Japan.
May be the best and most popular trekking destination around Tokyo is Oze national park which is located in 4 prefectures, Fukushima, Tochigi, Gunma and Niigata. 0.5 million people visited Oze national park in 2010.
Then, may be most famous among foreign tourists can be trekking in Yakushima island, located south of Kyushu. It became the 30th national park in Japan in 2012.
How about the gears? Should I bring them from my home? There are plenty of shops selling gears in Japan. The brand can be worldwide brand and domestic ones. Therefore if you do not have your gears now, you can wait till your visit to Japan and buy them in Japan. Just watch out of Japanese sizes. Men's LL is L or M in Europe. Also the shoes size is different. Japanese shoes size 28 means 28 cm and it is equivalent to European 44. Don't forget to wear or bring socks when you are going to the shoes store!