I love the concept of Sora. Showing us a different side of the world and the characters through a bird who’s always listening, who people feel comfortable opening up to. Brilliant! The descriptions of the world through a bird’s eyes are very clever and creative, and are a very interesting way of getting certain ideas across. ie. the development of Sora’s perception of Haruko.
As a non-human character, there’s only so much characterisation you can give him. But his impact on the world should not be questioned. Firstly, it allowed Yukito to continue to stay by Misuzu’s side in a form that wouldn’t cause her pain to be around.
Second, through his houjutsu power, Sora was able to make the puppet dance and stave off Misuzu’s despair, and even create an apparition of Yukito through the doll’s power to show Misuzu that she’s not alone and help her continue fighting the curse.
Third, he spent multiple days attempting to drag the the dinosaur doll out from the grass so that Misuzu might be able to find it, and eventually his efforts paid off when it was placed on the shrine altar and entrusted with the wishes of the townspeople, which eventually helped Misuzu stave off the curse a little longer.
And finally, when Misuzu eventually disappears from the world, Sora takes everybody’s hopes and dreams to the sky, as a chronicler, a messenger of the Earth to the heavens, in what I like to think of as an honorary winged one. He takes it all, returns to the sky, and after finding the original girl in the sky, they return to the Earth together as the boy and girl on the beach. None of the AIR Route would’ve been possible without Sora; Misuzu would’ve lost to the curse and died before Haruko could even come home. In that sense, Sora is very very important.