Very Best Friend. Suuuuure. You only think of her all the time, get jealous when she's with other girls, nervous when you're around her, blush when you see her, and don't want her being cute around anyone but yourself. Yknow very best friend stuff. Damn useless les...princess.
Hopefully, Izumi becomes Nanaki's wing woman. At this rate, Kurokawa's gonna develop or realize her own feelings and confess to Nanaki first.