A 15-year-old boy and 27-year-old woman find an unlikely friendship one rainy day in the Shinjuku Gyoen National Garden. These two broken pieces come together and heal one another as they learn what it is to walk.
The story takes place in a technologically advanced society in which robots can be programmed to behave like a complete human. A robot is asked to replace Hal, who died in an accident, to help Kurumi, Hal's girlfriend move on in life. "Hal" struggles to understand the real Hal's past, Kurumi's affections towards Hal as well as the meaning of being alive.