Byleth Eisner is the protagonist of the video game Fire Emblem: Three Houses. Originally a mercenary, Byleth becomes a professor at the Garreg Mach Monastery and is tasked with teaching one of the three houses of students. They possess a mysterious connection to the divine being known as Sothis, which grants them unique powers. Byleth plays a crucial role in guiding the students and shaping the future of Fódlan, the continent where the story unfolds. Their enigmatic past and leadership skills make them a central character in the series.