弾丸登山 (dangan tozan) refers to the act of people who, in order to catch the sunrise atop Mt. Fuji, start climbing from the middle point (5合目) in the middle of the night and then return back down immediately without rest.
Any of you planning to “do so someday” may like to know that this will very soon be unavailable in tour packages. Reason being that the government is discouraging travel agencies to plan such activities. This is because overnight activities without rest is already highly taxing on the human body. What more, mountain climbing is more exhausting than you think even if it is mostly slow-paced walking. To add on to that, without ample sleep, the body would have difficulty acclimatizing to the change in altitude leading to altitude sickness. With Mt. Fuji set to be officially registered as a World Heritage site, more and more people are attempting to make conquering the mountain a milestone in their lives and the crowded mountain would mean even more casualties in the dark, unfamiliar terrain.
To further discourage you from taking the risk at night climbing: did you know Mt. Fuji has an infamous spot where many people committed suicide? The area called Aokigahara, more commonly known as 樹海 (jukai) meaning Sea of Trees, is infamous for people wanting to end their lives because it allegedly has such thick vegetation, it is difficult for their bodies to be discovered. So if you don’t want to run into something in a different world, it might do you good to do a morning hike, though by the time you get back down, it would be really dark.
No! I’m not sharing my encounter! *shivers*