I've noticed a lot of doujin writers (and I find myself doing it as well) have Yukari in what seems to be in a downward spiral, where she falls for a brightly burning human (Yuyuko prior to death, or Reimu, or most of the time, one then the other), knowing full well she'll live on without them.
I read one where unrequited Yukari sits with elderly Reimu as she passes away, and there's so much pain in Yukari, it just breaks my heart.