Yoru Yoru Soba ni

Satoru is an insomniac, stuck in his own night as the rest of the world keeps turning. One night he meets the peculiar girl Mikoto, who claims her eyes see just fine at night but don't work during the day. She asks him to help her find a picture book she'd once read, a simple request that turns into an unimaginable journey for the two of them.

(Source: Lovely Strange Dark)