I've been going for the Yurei (Never Spotted) and Oni (Kill Everyone) medals on my first playthrough. What follows in the spoiler text below would definitely be considered a spoiler for Chapter 9 to a greater or lesser extent (depending on your opinion of such things) as my description will involve specifics of what happens in Chapter 9 from a story point of view.
That being said, I feel like the "event" I'm talking about in Chapter 9 shouldn't be a spoiler for you if you've been even vaguely watching the story cutscenes during Chapters 7 and 8, as the game tells you, in no uncertain terms, that you're going to have to do the "event" at some point! The only thing the cutscenes don't tell you is that it occurs
in Chapter 9.
If you're in any way concerned about spoilers for this game's minimal (but admittedly engaging) story content, don't click the spoiler text! Just don't do it! You won't be happy if you do!
Anyway, I think that's enough priming for even the most story-centric, spoiler-avoiding players so consider yourself warned if you open the spoiler text below!!!