That picture of Kiyo and Azumi was really misleading because the former looked very much like a girl and the latter looks a lot like a boy there.
Kiyo's pissed off that his fellow wheelchair b-ballers lack the competitive spirit because of their irreversible condition. He didn't choose to get that bone disease but he's trying his best to make the most out of it so I understand his frustration. Calling Azumi a baka's pretty mean though since she's currently trying to stop him from having to take the bus all the time.
Masaki's his own man and everyone just couldn't understand that. Nomiya's the only person who understands his passion for the sport and wants to play with him but he wasn't able to be there for him since he left. I hope that they both own those Basketball Club jerks.