Kousoku Otome no Seikatai

Kujou Hina is your typical girl who can sing worth a damn. After being struck with awe by the singing of two mysterious girls, she comes to a realization that, with the choker given to her by the mysterious girls, her song has the ability to eradicate evil spirits. Who are these mysterious singers that gave her the choker? Why was she chosen to have this power of song? In the pursuit of answers, she continues to meet others with similar powers.