[4] Byleth is a wandering mercenary who possesses the mysterious Crest of Flames and can wield the powerful ancient weapon known as the Sword of the Creator.

In Three Houses, they receive an offer to serve as a professor at the military academy of Garreg Mach Monastery, acting as the leader of one of its classes.

Ultimate was also met with hate from Western fans due to a perceived overabundance of Fire Emblem characters in Super Smash Bros.

[5] Byleth serves as a professor at Garreg Mach Monastery, and possesses the mysterious Crest of Flames; they can also wield the Sword of the Creator.

[7] Jeralt, suspicious of Rhea as the cause of Sitri's death, used a fire as cover to escape the monastery, and Byleth grew up under his care, but they still lacked a pulse and emotions, signifying that they were being kept alive by the crest stone.

When the villainous mage Solon traps Byleth in a seemingly inescapable void, Sothis is forced to merge her consciousness with theirs, making them the Enlightened One and causing her to retreat into their subconscious.

They are a rival to the main protagonist, Shez, who ends up being the one that attends Garreg Mach and allies with one of the three lords during the war, while Byleth, Jeralt and their band of mercenaries are hired by one of the opposing sides.

Epimenides then transports Shez and the three lords to a void and attempts to kill them, but they and Byleth work together to destroy him and escape back to their world.

[22] Brendan Graeber of IGN called Byleth "A Study in Simplicity", stating that "Byleth has a simple to grasp moveset with some fun small twists that's welcomely easy to learn the ropes with, and their unique approach to directional-based weapons stands out enough to make checking out yet another Fire Emblem hero worth it – even for the skeptics".

[23] Byleth was also met with criticism by Western fans, largely due to several other Fire Emblem characters already playable in the base game.

[24] Masahiro Sakurai, the creator and director of the Super Smash Bros. series, agreed that "there are too many Fire Emblem characters",[25] but also noted that he did not directly select the DLC fighters.

Ultimate competitive scene was mixed; Inverse commented shortly before the character's release that "it's not looking good for the Fire Emblem: Three Houses protagonist".