Seiryuu:
Seiryuu No Miko; Yui:
Real Name: Yui Hongo
Age: 15
Eyes: Blue
Hair: Blonde
First Appearance (Anime): Episode 1
Abilities: Priestess
Height: 162 cm
Blood type: AB
Birth date: October 26th
Affiliation: Seiryuu Seven
Yui is Miaka's best friend and the other girl that is pulled into the world of the book along with her. Yui and Miaka have been friends since childhood, though Yui managed to get better grades than Miaka and has her sights set on the high school of her choice, while Miaka must work to keep up with her. It is Yui's trip to the library to return a study book that triggers Miaka's discovery of the Book of the Four Gods that transports her and Yui to the world of the book in ancient China.
Yui is taken back to the real world soon after her arrival in the world of the book, leaving Miaka there to fend for herself. It was during this time that Yui kept reading the book, seeing its story spread out over the course of a few pages as Miaka was saved once again by Tamahome, took on the role of the priestess of Suzaku, and had many adventures on her way to Mt. Taikyoku to find guidance. It was also discovered that whatever Miaka experienced or felt in the world of the book was also felt by Yui. Miaka's cuts, injuries, and sicknesses were all transferred to Yui.
When Miaka attempted to wish herself back into the real world, Yui also lent a hand to her, concentrating on getting Miaka back. Strangely though, at that exact moment, Yui was pulled into the world of the book in Miaka's place, only this time in a different land. Alone and frightened, Yui was attacked by a group of men and passed out. When she came to, Nakago, one of the Seiryuu Seven was at her side. Believing she had been violated, Yui attempted to kill herself, but was unsuccessful. Nakago began to convince Yui that Miaka had abandoned her, and gradually as she recovered Yui came to believe it was Miaka's fault for her unfortunate fate. She willingly became the Priestess of Seiryuu and began to make her own plans to summon Seiryuu, in order to get revenge on Miaka for what she had done to her. Her anger at Miaka was a catalyst by which Nakago was able to further his own plans, and assemble the Seiryuu Seven to do his and Yui's bidding. In this way, Yui became Miaka's enemy, causing both of them great pain in the process.
To the eastern land of Kutou, where life flows with water, the maiden of the garden Seiryuu- Hongo Yui
---I found this on a site and just had to use it. However, I do not remember what site I found it on. If you write this, please contact me so I can give you credit!