Highlights:
Towa, Setsuna, and Moroha have learned that Rion is the daughter of Kirinmaru, and she holds the Kyuyokon root, which she offers to them.
The Kyuyokon is the ultimate weapon. It can absorb and expel unlimited amounts of demon power. It is the one thing that Kirinmaru fears. Rion asks the girls to slay her father.
Outside the barrier, Riku is holding off all the small-fry demons that are after the half princesses. While inside, the girls hear the history of Rion.
Rion lost her life 600 years ago and has been contained in the barrier of the Spiritual Mountain all that time. Kirinmaru refused to accept her death and kept her soul trapped in an astral body and sealed in Mount Musubi. He used the dream butterfly to meet her in dreams. Rion wants her soul free, and Kirinmaru's ambition to annihilate everything stopped.
When the girls, including Rion, exit the barrier after defeating the demon spirit beast, they encounter Sesshomaru. He questions Setsuna's use of the Yukari no Tachikiri. To strengthen her resolve to master it, he cuts down the dream butterfly that is keeping her from sleep. Doing this will cause the silver-scales to form quicker on Rin, which gives Setsuna much less time to save her mother.
Once Sesshomaru leaves, the girls meet up with Riku. Rion is happy to see Riku, but he is worried that Kirinmaru can see and hear everything thru him. Riku decides to take Rion with him, but before the girls can continue on their journey, Setsuna falls asleep.