9, 21, Katherine and/or Kasen

9 - Katherine has a difficult relationship with her dreams: for awhile after she lost her arm she had ptsd-esque nightmares and the phantom limb feelings would sometimes make their way into her dreams, so when she woke up from a dream where she did have an arm, she'd flip out when she realized it was gone.

:c

It gets kind of worse: alcohol has a tendency to decrease REM (dreaming) sleep and increase stuff like deep sleep, though that causes some level of dependance, so when she wasn't drinking before bed, her dreams and nightmares were sometimes very vivid.

Kasen on the other hand doesn't sleep nearly as much as a human or oni usually does: sort of as part of her "training" (Its more like method acting to some extent.) as a hermit, she tries to shed off a number of worldy desires, which includes stuff like rest. Given that oni in my head canon don't really need to sleep as often as humans, its easy for her.

I wouldn't be surprised that when she does sleep and thus possibly dreams, however, she either has no dreams at all, or stress dreams involving Reimu.

Or basically everyone else who frustrates her.

21 - Oh boy, this one is interesting. I can totally see Katherine start overthinking these.