Responses
I reread that chapter. You are right but the missing pair of earing was suppossed to be worn on the hunting but Emily lost it (chap 66). Now we know she gave it to someone.
Oh so then the blood basically acted as direction on who to target
Ohh if dark magic uses blood as a conduit then it makes sense that it activated to track Yurina bcs of the scratch Emily gave her using the earing. Maybe whoever she's working with made a copy of Yurina's earrings, only half is made to basically act as a lure and the other to control or be attracted to the other half.