Mount Musubi

 is a mysterious mountain that plays a major role in Hanyō no Yashahime. It is the objective for Towa Higurashi's quest to search for the Dream Butterfly to reclaim her twin sister's dreams and memories.

Season One
Sometime after returning to the Feudal Era, Towa asked Kohaku for information regarding the whereabouts of the Dream Butterfly. The new chief of the Demon Slayers searched through some texts indicating them inhabiting the mysterious mountain that resides in the east.

Several days later, Towa attempts to search for the mountain on her own after Setsuna had left earlier that morning. Unfortunately she ends up lost whilst encountering a mysterious man.

Towa later attempts to search for the mountain again, this time accompanied by Setsuna and Kirara. Unfortunately, she only finds a mountain that resembled an onigiri rice-ball.

Season Two
Many weeks later since the resurrection of Setsuna, the location of said spiritual mountain is revealed just outside Bokusenō's forest. They learn from the ancient tree that the Kyūyōkon Root can be located in a Demon Spirit Tree at the mountain. Towa and Moroha approach it, but are warned by Setsuna that it is cloaked by a strong demonic barrier, which was precisely why Towa could never find it before. From within the center of the center, lies a deeply sleeping deer-eared, red-haired girl on a swing or scale that emanates a pale greenish glow holds of a tree.

Towa, and Setsuna didn't get pass through the barrier except for Moroha. Later, Rion tells her that she is immune to the barrier. Moroha attempts to let them in. One of the voices they hear is from Kirinmaru, annoyed that Moroha got through it so easily. Rather than risk a battle from The Yashahimes and friction from Rion, he puts them to a test that they easily passed. He did not interfere when she gave them a Kyūyōkon Root.

After Towa gets a new weapon: the Zanseiken, they leave the mountain with Rion. But before that, the demons of Mount Musubi came and tried to stop them.

Trivia

 * Its name may be inspired by.
 * Mount Musubi is the second mountain to hold an important role in a main story, the first being Mount Hakurei where Naraku separated his human heart from his body.