Boundary of Sleep and Vigil

Story
The greater youkai of Gensokyo sleep a lot. Of course, that doesn't apply to all of them. Let's take a closer look at one of them―the sage, Yukari Yakumo. She sleeps at least twelve hours a day and even hibernates through the winter. It may seem far-fetched, but is her "sleeping" really just sleeping? What if she simply appears to be sleeping while engaging in something entirely different? What does the act of "sleeping" mean to Yukari Yakumo...? I plan to investigate the above and document my findings. It's too dangerous, you say? An investigation would be no fun without a little risk. Besides, information you can acquire without putting yourself in harm's way is not worth having. I shall outline my findings below...

As written above, Yukari Yakumo is a greater youkai and a sage of Gensokyo. Known as the "gap youkai," she is powerful, knowledgeable, and shrouded in mystery. One such mystery is that of her "sleep." In many worlds, Yukari is rarely seen sleeping and is more often seen to be awake and active. Perhaps it's just a matter of poor timing... Or it could be that worlds exist with Yukaris who can function on a small amount of sleep. That theory is worth investigating.

What happens when you're asleep? One obvious answer is that you may be dreaming. So what kind of dreams does Yukari find herself in? Does she watch on as images composed of memories and information are projected before her, just as we do? But then again, it's hard to imagine this youkai having such simple dreams, given how long she sleeps. Through sleep, she might see something different entirely or pass beyond some boundary. Having observed Yukari, she does appear to simply be sleeping, but it's an interesting idea nonetheless. There is one thing I should make a note of, even if it's just in my head―I feel like someone's watching me.

What happens after her sleep ends? What happens when she wakes up? In that moment, it may be that some power within her stirs, and she exerts some unseen force on her surroundings. In my records of the incident where spring disappeared, it says that she kept on yawing sleepily even after waking up and going back to sleep three times in quick succession. Perhaps Yukari is not so different from us after all... Maybe it's because I'm observing her sleep, but I'm starting to feel a little drowsy myself... This is no good. I'll continue my investigation after a quick snooze. Just then, a voice called out, "My, what are you doing watching me sleep? That's a rather shameless pastime, don't you think?" Yukari's eyes cracked open, and the next moment, she was wide awake.

Yukari had traversed the boundary between sleep and the waking world. Her arms and legs were still sprawled out upon the covers, but her eyes were fixed upon me. Or so I thought, but they were still shut tight. Fear gripped me, and time slowed to a crawl. ...Wait. How long have I been here watching Yukari sleep? I know it's a little late now, but there's no way I should still be here. That's right, I was just― "I don't mind playing with those who wander in lost from time to time," said Yukari. "Notes and observations about Yukari Yakumo's sleep? No such records exist... See?" And with that, the room turned to dust and disappeared into the void, taking all the records with it. "Goodnight," whispered Yukari.