Back at home, when he has time to examine it more closely, it quickly becomes obvious why this ritual never turned up in all his early research. It's not a typical soul summoning ritual. It's not a cultivation ritual at all; as Nie Huaisang puzzles through it, the closest category he can put it in is folk magic...not only that, but sex magic.

“Well, I don't see it,” Huaisang had said, and then he'd shoved his hand down the front of his pants right there in front of Nie Mingjue. “I—oh, I have the other thing now,” he said, and he sounded...intrigued. Nie Mingjue had quickly excused himself.