I would also be fine with an Airi-centric anime
But, I admit that playing the VN at the same time has helped immensely to increase my positive bias for her. Give me a likeable cast, fitting VAs and an *overall* nice story and I'm mostly satisfied. Heck, I've started to value a likeable cast more than most other points (i. e. the story can be as clisché and corny as it wants as long as it's not a complete "trainwreck")
@Shingo: I also felt that his study-tutoring suggestion was more like "I'll suggest this in order to respect your pride and point of view" than actually taking at at face value.
@"Main heroines" of the anime: Agreed on Airi and Miu, if only due to Shingo's blush and the glittery-sound effect *lol*. I'm pretty satisfied with Sakuno's sister role even though she could have a bit more screen time despite that she's not the most talkative person
. And for her to become a "main competitor" I feel there would need to be a (future) event to trigger her flag.