Kamui

A Mercenary from a distant nation hired by Valbar, Kamui used to live a nomadic life with his family and worked with grazing animals. However, they got into a scuffle with another tribe and lost, which led them to settle in a town. Unable to adjust to this lifestyle, Kamui set out on a journey, with his swordsmanship being honed due to his wanderings

After Barth is defeated, he joins Celica's party. After the war, he joins Jesse in building their own country in the lands that once belonged to Grieth. If Jesse is dead, he founds the country in his place.

(Source: Fire Emblem Wiki)