From MangaHelpers:

In this world, there are sirens who are able to control spirits through their singing, an ability which can be used for great good or evil. Haine is one of these sirens, though she has little confidence in her abilities. When she runs from her master one day, she meets a young woman named Madorasu who has escaped from her wealthy home. Soon, Haine learns the real reason Madorasu had been kept locked away... The manga continues with the story of the sirens, Haine and others who are a part of her life. [tethysdust]