There's something I keep thinking about. At the end when Koko leads Seiichi to the human part of the city, he accidentally bumps into the girl named Lune. Then Koko says that girl looks familiar. In Reiko if you ask Koko about her mother, she tells you her mother's eyes were brighter and more yellow. That matches the Lune's eyes. So there is a possibility that Lune is Koko's mother. Could it be?