Hinata & kageyama not being 'normal' friends like say, tsukki & yamaguchi are isn't new - they've always had a relationship that's unique to themselves. They're rivals but also partners who understand each other incredibly well. To someone on the outside, they do look odd

They spend every club session glued at the hip, if the team hangs out outside of practice they'll be together, they sit next to each other on the bus... But they dont eat lunch together, & squabble a lot. They're friends, but also not friends? Noone really gets it except for them

They have a very interesting and unique relationship that's not easily defined by one word, but ultimately it's very healthy for both of them and therefore it's very fun to explore!!