Yup, that is a big flame sac

Cute.

Only just recently learned that the central plot has to do with a basic tomboy office worker, so clearly the plot of this series has moved on beyond that (and marketable anime girls with monster girl characteristics)? It's a competitive market out there in anime world...
But for real, if Miss Kobayashi herself is somehow involved in this, it'll be... something, alright. Not gonna strain the writers for gaffs tho.