The Valley of the World Tree is a large valley that consist of not only the "World Tree," but also a coagulation of other plant life. According to Yae Tokiro, this is also her father's homeland, indicating that it might be populated. She wishes to travel to the valley so that she can bury her father's ashes. For a reason yet to be revealed, her companion, Sahara Sanjūrō, has too be searching for the World Tree.
Yea's father believes that the valley's existence ensures the inevitable restoration of nature.