The peace-loving kingdom of Hoshido strives to resist the expansionism of the kingdom of Nohr.
Corrin, a royal of Nohr and the player avatar and protagonist, lives in the Northern Fortress under what is essentially house arrest—until their father, King Garon, summons them to court and demands that they execute a Hoshidan prisoner.
Corrin refuses, and as punishment ​​for that insubordination is sent by King Garon on a mission to gather intelligence behind enemy lines. Deep in Hoshidan territory, Corrin learns the shocking truth that they are actually Hoshidan royalty by birth, and that Nohr plans to deploy an army of monsters in an upcoming plot to invade Hoshido.
Without time to process these revelations, Corrin is faced with a stark choice as their siblings from Hoshido and Nohr prepare to cross swords and demand they choose a side. Will Corrin follow the country of their birth, the country that raised them, or no country at all?

As the title implies, this game puts the fate of the protagonist squarely in the hands of the player. The story, the battle maps, and the characters who appear in the game are all decided by whether players choose to follow one of three routes: Birthright, Conquest, or the Revelation route that was later released as downloadable content.
This game features new tag-team and pair-up mechanics that allow units to enhance one another's capabilities, as well as Dragon Veins that allow royals such as the protagonist to alter the map's terrain in the middle of battle. There is also a base-building mode in which players can watch their allies interact in various ways within a castle of their own design.