Byleth is a playable character in the fighting video game, M.U.G.E.N Trilogy. The male and female variants were confirmed on January 20, 2020. In this fighting game, Yūsuke Kobayashi (Japanese) and Zach Aguilar (English) provide the role for the male counterpart, while Shizuka Itō (who also voiced Sakuya Izayoi, Japanese) and Jeannie Tirado (English) provide the role for the female counterpart, using voice clips recycled from Super Smash Bros. Ultimate.
Byleth Eisner is the main character of Fire Emblem: Three Houses, following in the footsteps of Corrin in also serving as a player surrogate. Unlike past player avatars Robin and Corrin, however, the only customizable features of Byleth are name, gender, and birth date.
In Three Houses, Byleth is the child of Jeralt Eisner, a former knight of the Church of Seiros. Byleth does not recall much of their past and Jeralt has told them very little; however, following a chance encounter where Byleth and Jeralt rescue Edelgard von Hresvelg, Dimitri Alexandre Blaiddyd, and Claude von Riegan from a group of bandits, they are brought back to Garreg Mach Monastery, where Jeralt is reinstated as the captain of the Knights of Seiros and Byleth is enlisted as a professor for one of the Officers' Academy's three houses: the Black Eagles led by Edelgard, the Blue Lions led by Dimitri, and the Golden Deer led by Claude. Depending on the player's decision, the story plays out differently.
Sothis is a mysterious entity who appears in Byleth's dreams and, eventually, manifests in real life, although Byleth is the only one that can see her. She has lost all of her memories except her name, but possesses great power, bestowing Byleth the ability to turn back time. Eventually, after Byleth is banished to a dark realm by a mysterious group called "Those Who Slither in the Dark", Sothis rediscovers her past and learns that she is a goddess; she merges fully with Byleth, thus granting them all of her power but ceasing to appear to them after that point, except in a few select circumstances. Sothis is also the source of Byleth's Crest, the Crest of Flames, which allows them to wield the Sword of the Creator.
Regardless of what house they choose, at the end of Byleth's first year as a professor, Edelgard declares war on the Church of Seiros and Byleth is forced to take a side. An accident results in them falling into a coma for five years; once they awaken, they reunite with their house of choice (or the Church of Seiros, should they decide to side against Edelgard after choosing the Black Eagles) and assist their house leader in their goals: Edelgard to destroy the Church, Dimitri to stop Edelgard, Claude to discover the truth behind Crests and the Heroes' Relics, and Rhea to stop Edelgard and Those Who Slither in the Dark.
How to Unlock
Scan Byleth's AR Icon from the M.U.G.E.N Trilogy website.