The story takes place in Alberia, the kingdom where dragons live. All royal members in Alberia have the Dragon Transformation ability, where they can wield a dragon’s power by forming a pact with a dragon to borrow their form in battle. One day, a strange occurrence begins to happen in this kingdom. The Holy Shard protected by the capital starts to lose its power. In order to save his people, the Seventh Prince, who has not made a pact with a dragon, sets off on his Dragon Selection Trial.
Source: Wikipedia, "[en.wikipedia.org/wiki/Dragalia_Lost Dragalia Lost]", available under the CC-BY-SA License.