so I hadn't thought about this before but;
I think having Genioh Yamashirogumi's soundtrack really makes Akira to a not-small extent. The distance from being purely Japanese motifs fits the "this isn't the Japan where you're watching this movie," and yet it's NOT futuristic sounding at all - a little like how Star Wars' soundtracks tell you it's NOT science fiction, it's larger than life romanticism, Akira's soundtrack tells you it's about human conflict, growth and interaction.