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.

Wei Wuxian doesn’t let the Wen Remnants hand themselves over after Jin Zixuan’s death. Instead he makes one last sacrifice to ensure they survive. Months later, a Lan cultivator kneels at the edge of the Burial Mounds, ready to offer himself to the feared Yiling Patriarch. Or: Sacrifice is an old magic, but love is even older.

“Well I have to entertain myself somehow while His Excellency is off tending to official cultivator business all day,” Wei Wuxian says with a pout. “Besides, crafting talismans to show your husband just how good he makes you feel isn’t against the sect rules. I checked." The twinkle in his eye is shameless, and Lan Wangji loves him for it. - In which Wei Wuxian makes a sensory-sharing talisman and Lan Wangji makes some self-discoveries.

The fault, Nie Mingjue thinks later, lies squarely with the blasted weather.

Nie Huaisang would do anything to help his brother. Now he knows the very thing required, and it forces every choked, desperate thought to the surface. Everything hiding beneath 'Da-ge smiled at me' rises forcefully up through him so that his mouth is filled with the taste of wanting. Yes, Nie Huaisang would do anything to help his brother, but especially this.

The resentful energy occupying Wei Wuxian's body like an enemy army is very interested in giving him Lan Wangji, tied up with a bow. Wei Wuxian is hoping that Lan Wangji (who is far too noble and very keen to save Wei Wuxian's misguided soul) doesn't find out about any aspect of that.