Lan clan forehead ribbon responding to soulmate
What if, Lan sect’s forehead ribbons channel the spiritual energy of the wearer, like their swords. While most cultivators never reach a high enough level in their teens to bind their ribbons, the twin Jades were an exception.
Once a forehead ribbon is bound by spiritual energy, it can’t be undone by anyone other than self or those in front of whom they need show no restraint. No one should have been able to take off Wangji’s ribbon - no one other than his family or cultivation partner.
Once a ribbon identifies a person as one’s soulmate, it responds to that person’s touch and gets undone. But it was a very rare occurrence. It meant that the ribbon was yelling to the whole world that Wangji was in love with the perpetrator. How could his ribbon betray him in front of the world, when he himself was unsure!?