Keiko lived with her Grandfather, as both her parents had died some time before. They were attacked by brigands in their home, killing Keiko's grandfather for his insistence that they had nothing worth stealing. Before they can try to force anything from Keiko, Jei arrived and easily slaughtered the thieves. Jei took a spear that was wielded by one of the deceased men, claiming it as his own and imbuing it with dark power. He turned to Keiko, about to kill her as well, but stopped. He said that she was innocent and spared her life. As he left, Keiko's house was slowly burning down from a fire that started during the battle. With nowhere else to go, she followed Jei into the night.
Keiko always calls Jei "uncle", and he calls her "[his] innocent". Her relationship with him seems naive to the point of disturbing, believing that Jei is truly an agent of the gods. Even when the two are separated, she happily discovers the bodies of Jei's victims as a trail to follow to him.
When Jei felt the calling to find the Kusanagi, being held by Usagi, Keiko followed. She was present during their battle, and when she nearly came to harm, Jei was distracted enough to be run through with the Grasscutter blade by Usagi, apparently destroying him.
Keiko vanished after the battle, only to reappear at Inazuma's side, calling her "auntie". The two travelled together for some time, until Jei's spirit was exorcized from Inazuma's body, killing her in the process. Keiko once again vanished and reappeared, this time at the side of a man named Hama who had survived Jei's massacre of his temple, the apparent new host of Jei's evil spirit and Keiko's new "uncle".