Assistant in evil to Yakumo's biological father. Miyuki is shown as being physically strong mentally twisted and very loyal to Yakumo's father.

Spoiler

Miyuki is the person who Yakumo's father uses to affect the physical world. Nanase Miyuki is the real culprit in the Nanase Quadruple Murder. She killed her family because of the emotional and physical abuse she received as a result of being born from an incestuous relationship between her mother and her grandfather. She loves Yakumo's father and longs for his love. Although she knows he views her as a tool to do his will, she still follows him because his influence led to her freedom from her family.