For everyone saying she's the mastermind,
Things pointing to it:
-she's smart
-she has two leaves on her jacket, but across 2 hair ribbons it's 4 leaves
-she is
very attached to Yotsuha
-her eyes are cropped out a suspicious amount this chapter
-she's in the perfect position to frame Yae and cover her tracks
Things pointing against:
-Yotsuha has already told her what happens in the future at an early enough point it's not reset by her going back in time. With that much warning, Fuu would've changed the plan enough for Yotsuha to notice it doesn't match up with the future
-the future already happened, so if Fuu had already indeed manipulated everyone including Yae and Yotsuha into killing Uichi, then Yotsuha would already have an inkling it might've been her
-we still don't know how Yotsuha got her watch
All in all,

.