The Plains of Hoshido is a location in Fire Emblem Fates. It is a critical location in the story as the story path changes from here.
The Plains of Hoshido is a wide open Hoshidan plain situated near the boarder between Hoshido and Nohr. While the field is vast, a river flows through it with several bridges to allow safe passage. Wielders of the Dragon Vein ability can dry the river however.
This field is also the chosen location for any battles against an amiibo scanned character.
The Plains of Hoshido first appears in the prologue of Fates where the Avatar has a vision of a battle between Hoshido and Nohr in their dreams. Though they team up with the Hoshidan siblings to take down some Nohrian soldiers, the two royal families meet, both beckoning the Avatar to return to them. However, before the Avatar can choose, they are awoken, leaving them to wonder if this dream was something important to come.
Later, after the destruction of the Shirasagi Castle Town and the murder of Queen Mikoto by the plot of King Garon, the barrier protecting Hoshido falls and the Nohrian army begins their invasion. Mobilizing all troops, in Chapter 6, the Avatar's vision comes true as they find themselves in the position of having to choose between joining the Nohrian adoptive siblings they grew up with or the Hoshidan siblings who are their siblings by blood.
The Avatar chooses to stay with their rightful family by blood in the Birthright version of Chapter 6. While Xander asks them to reconsider, the Avatar refuses as it was King Garon who caused the deaths of so many innocent Hoshidan civilians as well as the death of the peaceful Queen Mikoto. With the help of the Hoshidan royal siblings, the Nohrian army and the royal siblings are forced to retreat.
The Avatar chooses to return to his Nohrian siblings in the Conquest version of Chapter 6. The Hoshidan siblings are shocked by their choice and plea for them to reexamine the people they are returning to. However, the Nohrian siblings protect the Avatar and force the Hoshidan army and the royal siblings to retreat. Upset that they had to betray their true siblings, the Avatar steels themselves as they need to return to Nohr in order to get answers from King Garon.
Conflicted and ultimately unwilling to battle either of their families, the Avatar is forced to watch as the two armies fight in the Revelation version of Chapter 6. Wanting to seek a more peaceful solution, they plead to the eldest brothers of both families to listen to them. However their pleas fall on deaf ears, as both brothers continue to fight to prove that their side is right. Needing a way to catch their attention, the Avatar, Azura and their retainer decide to take down the lead captains of both armies. Unfortunately, both Ryoma and Xander takes this action as a betrayal of the Avatar. With both armies now branding the Avatar and Azura as traitors, they are forced to flee to safety.