Haikyuu!!

i love having mismatched merch for characters, like here's kuroo tetsurou (18) high school volleyball player and his good friend bokuto koutarou (18) high school volleyball player

We don't even know he has a sister until that point whereas other characters' siblings like Natsu, Saeko, Akiteru, Alisa have all made appearances way before then. Even Oikawa's sister, though we don't see her, we at least know she exists because of Takeru.

He's both closed off to us (the audience) as well as the other characters in the series, and this results in them finding him rude or disliking his character in general (see: the "Kageyama is abusive" discourse that somehow keeps popping up even now).

Chapter 387 takes place in 2018 and was published in 2020 so it takes him 6 years of in-universe time and 8 years of irl time to really open up.

And the catalyst for all of this is Hinata fulfilling his promise of beating him.

You see, another thing to note is that, whenever Hinata thinks of Kageyama, he's always looking at him from behind.

His internal image of him is someone who's always up ahead, someone he needs to catch up to, meaning Hinata can only see one side of him, he cannot see all of Kageyama until he catches up and passes him.

Which he finally does here.

In this shot Hinata is finally the one who's looking back at Kageyama. At this moment, Hinata (and by extension the audience) can see him for all he is, can see how he was just a lonely boy who's been waiting for someone to meet him where he is, to keep running alongside him and not quit the race.

Someone he doesn't have to go easy on. Someone who would actually tell him to hurry up instead of slow down for a change.

His someone better.