Smargs won't Sing

Around three years ago, a village was destroyed by an evil Smarg (magical creature), in this case, a dragon. The sole survivors of the massacre, the sisters Chloe and Iria, fled to a nearby village. The younger sister, Chloe, doesn't speak, but is a friendly and diligent worker who is loved by all. The older sister, Iria, is disruptive, rude, and cruel, especially towards the unfailingly loyal Chloe. But how did two young girls manage to escape such a powerful creature in the first place? Is it possible that one of them made a pact with the Smarg? (Source: MangaHelpers)