Those are the 4 winds (from lowest to highest) Shyrokko, Leveche, Mucira and Chamsin and her cousine Polarlight.
In life, Polarlight was siren and nice, but now she became shizophrenic and her dark ego wants to kill her cousines. Here the reason why...:
When The 4 Winds were rising from the grave as Silencers, the four girls didn‘t notice, that Polarlight was alive again too, because they didn‘t hear her scream (she couldn‘t, because of the hole in her neck and her trachea. Down there she suffocated again and comes back to the World of Death as a Demon. Since that moment, she is shizophrenic. Her normal ego acts the way, she did in life, but the dark ego wants to kill The 4 Winds, because they left her suffocating in her own grave. So, The 4 Winds returned, because Shodai told them, that her cousine is alive too.The dark Polarlight was standing in front of her grave, bleeding at her neck, and pressing her hand against it, so that she can breathe. She asked the four, why they left her diing in the grave. Than she attacked the four girls. First, she killed Chamsin, who didn‘t want to accept, that she would kill her. Than her normal ego appeared, and the three told her, that she had killed her beloved cousine. She falls down to her knees in front of Chamsins dead body and started crying. In this moment, her ego changed again, and killed the other three too. Than she disappeared, and after a few minutes, The 4 Winds woke up as demons.

They belong to ME!