A plate is mentioned as the object Futo used to transfer her soul into in order to become a shikaisen, and she seems to carry several plates in Hopeless Masquerade.
For ULiL, this meant Futo's associated urban legend was that of Okiku and the Nine Plates, though Kisume appears to have adopted an Okiku motif too within this story.
I thought Miko was mad about Futo breaking a plate, but this makes more sense.
She might very well be; I was just explaining Futo's general association with plates. Since she throws them in some of her spell card attacks, she might've broken this one too.