The blue sky stretches on, endlessly——

Gazing up at a sky of pure blue, cloudless and bordering on nothingness, the boy — Mochizuki Sora — lets his mind drift into the past. Over and over he revisits the smile of the one girl he ever wanted by his side, killing something inside himself with the weight of his own sins. Whether from freak weather or some shift in the heavens, the clear skies had already held for a full week.

And yet, he knows — that even under a sky without a single cloud, rain can still fall.

What fills the heavens is a blue so vivid it borders on eerie. What that blue means, and what awaits beyond it — he cannot say. The heart of a boy who has left himself stranded in the past remains imprisoned by the sky.

And then, as he slumps alone on the rooftop, a girl appears before him......