Kusotori
Mori Calliope’s pet name for Takanashi Kiara.
The phrase is from the words クソ<Kuso>Damn, shit, utter trash and 鳥<Tori>Bird and means "Damn Bird"
Kiara: "Hey Callie wanna hang out?"
Calliope: "Not today Kusotori, I have a stream scheduled.