Do I have to pay an entrance fee to visit Mt. Fuji?
Much of Mt. Fuji belongs the Fuji-Hakone-Izu National Park, but no compulsory admission fee is charged so far for entering each regional park in Japan. This is largely due to the current legal system concerning the nature conservation and public use, and it may change in the future as the demand seems to be growing in order to secure the descent public amenities and services.
In the meantime, "contirbution fee" has been implemented in Mt. Fuji, for which each visitor is requested to pay at each major trailhead (at one of 5th Stations). There is no legal obligation to pay this and no additional reward is given in turn so far, but it is simply reccommended to donate if you could appreciate all the benefits you enjoy.
The collected money will belong to each prefecture (Yoshida for Yamanshi, and other three for Shizuoka) and be used to improve the security in the mountain.
Note, however, there are normally charges for using parkings and shuttle buses, besides the toll road to access the Yoshida trailhead.