I've got three mountain stories to share.
First story: An acquaintance of my parents is into mountain climbing. Apparently, this is a story he told. He’s a hardcore enthusiast whose hobby is what they call "route finding"—trekking through areas where there are no established trails. According to him, if you go deep enough into the mountains, you can see things scaling sheer cliffs at incredible speeds. Naturally, whatever those are, they are definitely not human.
Second story: When I was in college, I joined the wandering and mountaineering club. A senior member told me about an incident when he was on a snowy mountain and had pitched a tent inside a mountain shelter. In the middle of the night, despite a raging blizzard outside, he heard the clanging sound of someone taking off crampons (the iron spikes attached to climbing boots for snow). After that, nobody came inside. There is no way anyone would be handling crampons outside in a midnight blizzard. And it makes no sense that they wouldn't come in. According to my senior, the spirits of lost climbers wander around in forms like this.
Third story: After I started working, I had some free time, so I joined a working adults' mountaineering club for a while. During my time there, I nearly got lost in a disaster and was so terrified that I quit climbing ever since. The near-disaster happened when we went ski-mountaineering into the Azuma mountain range in Aizu. We entered the mountains trusting the forecast that the weather would clear up, but it never did, and the blizzard just continued. We should have stopped the climb right there, but our party of three had gone too deep and fell right into a whiteout, losing our path. Before we knew it, dusk was upon us and night fell. To avoid freezing to death, we had to push through the forest without sleep, wandering around until very late at night. As a side note, when humans are pushed to extreme limits, you start seeing hallucinations. In my case, I remember being thoroughly messed up because I kept seeing "houses" on the other side of the trees. I’d think, "Oh, there's a house," and walk toward it, only to find just more forest... That is a pretty unnerving experience. The member walking in front of me was getting angry, and the things the member behind me was saying started losing all coherence as time went on. Honestly, it's a completely miserable memory.
After that, we found the Keio Hut and our lives were saved, but the next day, which dawned crystal clear, the Self-Defense Forces were dispatched for search and rescue operations. Because of the previous day's bad weather forecast, quite a few people besides us seemed to have been trapped in the snowy mountains. According to the old man who ran the Keio Hut, among the people heading toward the hut, there were some who "never arrived." I don't know if it belonged to one of them, but we heard a report that right in the middle of the path leading to the hut, a single ski was found stuck upright in the snow. In the middle of the night, when skis are your only means of movement, there is no way you would ever stick one upright in the snow like that. Especially just one... You would never let go of skis that your life depends on. Call it a gut feeling, but... I think the owner of that ski probably saw something right at the very end, or lost their mind. Out there, it wouldn't be strange at all for something like that to happen.