In his youth, Byleth travels Fódlan as a member of a mercenary band led by his father Jeralt, earning widespread accolades for his strength and skill. But a chance encounter with three students leads him to travel to Garreg Mach Monastery, at the center of Fódlan, where he becomes a professor at the famed Officers Academy.
After spending a year imparting his experience and tactical acumen to his students, the whole continent is suddenly engulfed in war—and Byleth throws himself into the fray to protect his charges. With the aid of the Sword of the Creator, a relic weapon said to have been wielded by an ancient hero, and the time-manipulation powers of the mysterious Sothis, Byleth is able to lead his allies to victory and guide Fódlan into a new era.