Blood Soul Nightmare Entry was a good technique. Through it, she had obtained a great deal of information about the Shepherds from Kaishoku Shugaku.
After calming Yuria down, she had originally planned to harden her heart and kill Kaishoku Shugaku. Even if she didn't kill her, she'd intended to leave her a vegetable. But in the end, she merely altered Kaishoku Shugaku's memories again and directed her to return to Kawamori. It wasn't out of mercy; she was hoping to learn more about the Divine Gate in Kawamori that way.
According to what she'd learned from Kaishoku Shugaku, the Shepherds' apparent expansion outward from Kawamori was a smokescreen. Their actual core forces were still operating in the Kawamori area. They'd done this to divert the Divine Gate's attention, allowing the spy they'd planted inside the Kawamori Divine Gate to work with their people in the area to carry out an "important operation."
The Shepherds knew that the Divine Gate in Kawamori had discovered the spy and was conducting an internal investigation. This operation would temporarily hinder the Divine Gate's efforts to hunt down the spy, allowing the spy to serve one last purpose before being fully exposed.
As for the so-called "important operation," Kaishoku Shugaku only knew a little and had no concrete information. She guessed it involved a Blood Sacrifice powerful enough to overwhelm the Divine Gate and break the seals on several Gates of the Underworld at once. There were six Gates of the Underworld in the Kawamori area, and their sheer number had always left the Kawamori Divine Gate feeling overwhelmed.
Just as its name suggested, a Gate of the Underworld was an entrance to the underworld. Sealed within each one were extraordinarily powerful spirits, almost all of them "Dragon"-class. The few exceptions were even more powerful