Full book reveals that it is Kasumi's cat ears headband, the weapon of mass destruction, Big 7's bane. Don't ask me why she has it.
lean in
snap
glare!
paant
paantYou're facing off against a battleship...Shit...!!No matter how much of a pervert the opponent may be... right?Yes, indeed.As a destroyer, one must show courtesy.So I've had something special prepared for you.Nagato-san, I'm well aware that you're not going to blab so easily.Aye-aye!OOSHIO!
THAT, PLEASE!!!Some... something special..?Asashio!Stop that, Michishio.