3 years ago, Yoshiko and Riko were just... strangers. Strangers who were dragged to the shrine every week by their mothers. Their mothers constantly conversed while both of them hid behind their mother's back, just like any kid would do in an unknown environment.
Every week, they had this same routine. Nothing was ever different, nothing ever changed. However, this endless loop was making Yoshiko quite bored back then. She could be summoning demons in her basement, she could be searching for places to do rituals. Yoshiko decided to find someone to be her partner... her "little demon".
And Riko was the right subject. One of these weeks, Yoshiko peeked from her mother's back and slowly approached the hiding Riko. Then, everything went in place.
Yoshiko asked Riko if she wanted to go around the neighborhood finding demons. Riko, scared but confused, accepted and they went on their little journey, they keep going every week, their bond getting stronger. Riko finally had a friend in Uchiura, she thought. Back in Tokyo, she was shy and felt out of place. Finally here at the small district, she had someone to have fun with. A friend.
Yoshiko on the other hand... didn't have the same feeling.