I'm thinking they were for a play. I was kind of waffling on whether they were "stone masks" or "jewel masks". The latter being, y'know, like the things you would see people wearing at masquerades. But when I plugged the kanji into Google, the results were overwhelmingly actual stone masks (mostly from Jojo's Bizarre Adventure), so I decided to stick with that.
Inb4 "is this a Jojo reference?"
Uwawah!
Kinjou-san!?
Look ou-...!!Cultural Festival Props
Stone Masks*Clatter*I'm fine, I said~ (lol)
I'm taller than you any...Boowha! The dust!
*Cough...! Cough!**Poof...*32nd
Graduation Art Project*Cough cough**Wobble...*Cultural Festival
Costumes