Theory time. I always connect this manga with Alice in wonderland, so far so good. In Alice story, at 1 poin Alice become Evil queen favorite hostage,, So my theory is, a demon Musica is run away princess, she give Emma a necklace, what for? So when Emma got capture by demon, they will notice that necklace from Musica, so demon not just kill emma, but they using emma to search Musica. Just like Nami with Lola vivrecard case.