Siren is one of the four main cures in the series. She is Hummy's childhood friend and singing mentor, both born and raised in Major Land. For years before the series started, she was Major Land's Fairy of Songs and sung the Melody of Happiness every year. However, for the current year, Humy was chosen to sing it instead. She, allegedly feeling betrayed, traveled to Minor Land to ask to become Mephisto's subordinate. In truth, she was brainwashed to function as a tool so that he could complete the Melody of Sorrow.