Kageyama stares as Hinata ran over to him, holding his arm as tears trickle down his face. Ruffling the shota's hair, he asks him what was wrong, and tells him to 'quit blubbering, dumbass', though both know he means 'stop crying, you aren't allowed to be in pain'.
Hinata mumbles something about it being a bee sting, which puts Kageyama into an awkward situation, because who would expect him to know what to do for those? The setter isn't exactly a doctor, after all.
He ends up taking the sniffling Hinata to Suga in the hopes that the ashen-haired third year will know what to do. Suga being Suga, and the team 'mom', sits Hinata down and send Kageyama to get the first aid kit and some ice. He does so, willing to do anything to relieve Hinata's pain and stop those tears that were bring an unfamiliar lump to the ravenette setter's throat.
When he returns, Suga takes the ice pack and presses it to the sting, all the while murmuring soft, comforting words; and a still more unfamiliar feeling begins to gnaw at Kageyama's stomach. He recognizes it, despite its foreignness: jealousy. He is jealous that he isn't the one comforting Hinata and making him feel better. And it really, truly hurts.
He watches carefully every move Suga makes, hears every word he says. Attentively he watches the movements of Suga's deft fingers putting some sort of cream and a band-aid on the hurting elbow. Hinata gives him a curious look as to the careful attention Kageyama is giving him, but says nothing.
Later, however, Hinata wraps his arms around Kageyama and whispers that he's all right, it's just a bee sting, oh, and don't be jealous of Suga, that he will always stay with Kageyama. Kageyama is surprised at the shota's correct interpretation of his gaze, but that's less important.
What is important is that Hinata is his, and he is Hinata's, and so it shall always be.