For the audience, Menma is visible. She is vibrant, loud, and glowing. But for most of the characters, she is nothing but air. This creates a profound sense of dramatic irony and frustration. We see Menma trying desperately to interact with her friends, only to pass through them.
Contrasts Jinta’s supportive, non-interfering father with Menma’s paralyzed, grieving mother. Anohana Episode 8