The story of "the brother and the sister."
Which Dreamed It is the sixth chapter of Subarashiki Hibi. Mamiya Hasaki's perspective chapter. The one person who shoulders the memories of a certain incident.
We're given a glimpse into the forgotten past, where everything truly began.
The tale of a young girl who's deeply attached to her brother. She always believed in that promise with her brother, under the Hill of Sunflowers.
Which Dreamed It only has one ending, the Which Dreamed It End.