Mountain climbing to Mt. Fuji is particularly popular in Japanese sightseeing. On July 1st, it’s the first day for the mountain climbing season on Mt. Fuji, however, a rainy season called “Tsuyu” continues until around the first half of July. I believe everyone wants to climb it safely when it’s not raining but on a sunny day and enjoy the beautiful scenery if possible.
It depends on the year but sometimes the rainy season “Tsuyu” is not even over after July 20th. I recommend mountain climbing after the rainy season is over. In addition, you better avoid the weekend and holidays called “Obon” in August to go because it will be very crowded.