The scholars fo the Asako family theorized that somewhere in Mori Isawa lied a passage to the Spirit Realms which they called the Heart of Nature. This passage touched on many different realms including Chikushudo, Sakkaku, and even Yume-do. The portal did not have a specific location, but instead moved throughout the forest. One could not predict to which realm the passage would open. Even those beings of the Spirit Realms who wandered through the passage had no way to know how to return to their home realm unless they were being aided by other magics. The passage was guarded by the elemental spirits called Yuki no Onna.