Shin Shiyou (Chinese: 秦詩瑤 Qin Siyao) is a spiritualist and a holder of Nenyou constitution who was chosen as the fiance of Ki Tanmoku due to her powers that can heal the Youmeishi. Knowing that the spirit shadow will have a close relationship with his master, she is jealous of Keika You and Ki is always cold towards her. Even so, she trusts Keika and calls him the strongest spirit shadow. She is fiercely loyal to Ki, supports him and understands that he toils with his position.
Shiyou is an attractive young woman with mid-back length brown hair, violet eyes and thin eyebrows that are shown to be visible under her fringe.
However, behind closed doors, she is an otaku who is almost the exact opposite as her "outside" appearance.
When Shiyou was a little girl, she was chosen as the suitor for the Tanmoku family's heir named Ki Tanmoku. She had always loved him so where she was ecstatic to hear that she was to marry him. Etiquette classes, gymnastics classes, and tutoring were among the many things she took on to be a suitable woman for the young heir. However, he mainly showed no interest in her and he did not seem to appreciate her efforts to please him (which would cause her to be easily persuaded by and evil spirit in Episode 2). Throughout the years, she remained happy where she never lost sight of who she was and her love for Ki.
Shiyou first appears in Episode 2 when she arrives at the airport with her suitcase before removing both her sunglasses and hat for airport security. 
- What’s the point of a contract on a scrap of paper (2)
- It was inevitable that I would be attracted to him by the flow of time
- My only mission is to remove my clothes for him
- Pride disappears the instant you truly begin loving someone
- Gross, did you wet yourself over my lecture earlier?
- I would definitely rather die than have him see me like this, obviously!
- He has always been out of reach for me. Our fate was decided from the beginning. He is always the star. I am just a member of the unnamed audience.
- Why do you only ever show me your back?