As part of the "Atelier" series of games, it is the third installment of the "Dusk" story line and the 16th main game in the series overall. The game's story takes place about 10 years after the beginning of Atelier Ayesha: The Alchemist of Dusk and 6 years after the beginning of Atelier Escha & Logy: Alchemists of the Dusk Sky. As water sources dry up from an oasis town, the plants wilt and animals go hungry. It is here where two alchemists with different methods of making a living meet. Whilst Shallistera aims to find a way to save her village from demise, Shallotte Elminus goes on her daily life in an attempt to become a proper alchemist. Shallistera's story will reveal the truth and mysteries that have been depicted throughout the series, while Shallotte's story will revolve around the daily life in the world.
Source: Wikipedia, "Atelier Shallie: Alchemists of the Dusk Sea", available under the CC-BY-SA License.