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.

History
600 years ago, after Rion was killed by Sakasa, her soul has been trapped in this astral body and sealed in Mount Musubi. Eventually, Kirinmaru used the Dream Butterfly and forced her to meet him in dreams.

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 Mount Omusubi, a mountain that resembled an onigiri rice-ball, but even though the old farmer has never heard of the name of Musubi before.

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 qilin-eared, rubine 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 Half-Demon Princesses 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. Rion have continued to befriend the Half-Demon Princesses and want to slay her own father the Lord of the Eastern Lands. Rion tells them that she was dead 600 years ago that her father did not accept her death. Also Rion warns them of the Degenerate Age since Kirinmaru traveled every corner of the world except, beyond space and time which means the future that Towa was living.

Kirinmaru is after the spirit named Akuru and capture him so he can move the Windmill of Time until it will cease to exist that they were surprised as what the Spirit of the Tree of Ages said. Towa hugs her in pain that she's all alone, Rion was surprised and said that she's a kindhearted person. As they find a way to save Rion, when suddenly, Setsuna had sensed the between her and Kirinmaru has continued for 600 years and tells her to sever it. Rion will send into the afterlife that'll stop Kirinmaru's tyranny and Setsuna agreed, so she cut it as Rion's Dream Butterfly have been sliced, then the cocoon has fall apart and seen of the vessel from Rion's soul made from her bones and grave soil. But then the aura of Kirinmaru came out of the doll and tells her that its dangerous for her to leave it there, and back inside the cocoon so she'll never leave Mount Musubi, and forced her back inside the doll. The eyes and mouth are glowing, her head is cracking and she's about to move to use her bones and grave soil, so she'll rise again and walk on her own strength. Rion use the Kyūyōkon Root to dismantle the barrier as the Kyūyōkon Root produces the Hoshikiri no Fue. She plays it for her memory of her father took her around the world and give Towa the Star-Slicer Flute. Rion asked them to journey with them and Moroha answered sure, like they all say, "Any trip worth taking's worth with friends." and Towa welcomes her.

But Setsuna sensed the demon energy that shrouded this entire mountain and it's heading this way called the Demon Spirit Beast. Towa plays the Hoshikiri no Fue and it turns the new weapon: the Zanseiken, she uses the Sōtō no Sōryūha to defeat the Demon Spirit Beast. After that, they leave the mountain with Rion, as they start heading back to Kaede's village, Sesshōmaru and Jaken have arrived.

One month later, Rion returns there, with Riku at her side, in "Kirinmaru of the Dawn", and in flashback from Moroha as what Rion warns them about Akuru and the Windmill of Time. In "When the Grim Comet Falls", Riku and Rion arrives at Mount Musubi, as this is Riku's first time entering Mount Musubi without the barrier and since he has the apple seed from Towa that he had a first met. After they plant it, Rion chants to the mountain to grow another Kyūyōkon Root, and it works, spawning a green apple. When suddenly, they saw the Grim Comet from that the Degenerate Age is about to begin and they leave, ready to stop Kirinmaru.

At the behest of Inuyasha and Kagome, Kohaku and his yōkai taijiya, along with Sango, her twin daughters Kin'u and Gyokuto, two tanukis Hachiemon and Takechiyo, Hisui, and Kirara, on the outside of the mountain, and Miroku and Kagome Higurashi inside the mountain are preparing to contain the Grim Butterfly within a barrier. Kohaku and the yōkai taijiya launch Gyokuto's demon repellant powder from the catapult to force the Grim Butterfly to move as they want, lighting up the first three seals. Kin'u throw her sacred sutras at the butterfly, but it begins to escape from the barrier before Sango uses her Black Hiraikotsu to get it back on course, lighting up the fourth seal. With this, Kagome uses three Sacred Arrows to immobilize the butterfly and Miroku chants to light up the fifth seal from the mountain, activating the barrier to restrain the Grim Butterfly.

After the reveal of Rion's true feelings, the Grim Butterfly begins to calm down. Outside the barrier, Kohaku commends Towa, Nanasuke and Rokuta cheer, Hisui wonders if Setsuna is alright, Kin'u, Gyokuto and Takechiyo all cheer that they have been successful, and Sango wonders that they've been saved from the Degenerate Age. Unfortunately, when Kirinmaru's second incarnation, Osamu Kirin haunts Rion using her tragic past, the Grim Butterfly begins emitting miasma, causing everyone on the ground to panic. After Rion fights back, the miasma stops, and as the sword of Amatsumikaboshi ascends to heaven with the spirits of Kirinmaru and Rion, the Grim Butterfly dissolves.

Trivia

 * Its name may be inspired by.
 * Mount Musubi shares similarities with Mount Hakurei;
 * Both had a strong spiritual energy barrier surrounding it.
 * Both were used to conceal an important character: Naraku and Rion respectively.
 * Both had an important role in their respective stories. In the original series, Naraku used it to hide away in order to discard his human heart and finally destroy Kikyō. In the sequel spinoff, Towa had sought the mountain out to find the Kyuyokon Root that Kirinmaru feared.