If the closeup from behind on page 5 seems odd to anyone, note that Japan has an idiom where the perception of a person having a "broad back" means you see that person as dependable and manly.
Like, you get surveys where women say a man's most handsome trait is his back and shoulders seen from behind (背中), and that's meant to be a compliment.
Anyway, here, it's a shorthand way of showing how much lil' bro respected and admired big bro (and maybe some BL feelings, you never know).