Name: Byleth Eisner
Age: 20-21 (Pre-Timeskip);
Species Human/Deity (story-depending)
Occupation: Teacher at Garreg Mach Monastery
Interests: Helping and listening to people, likes swords, reliable allies, smiles, and being trusted, and has no apparent dislikes.
Born to Jeralt and Sitri on the 20th of the Horsebow Moon 1159, Byleth lost their mother shortly after their birth. She was buried at Garreg Mach Monastery. Some time after her death, Jeralt left the Knights of Seiros, taking his newborn child with him to travel Fรณdlan, becoming a mercenary in the process and starting his own mercenary company.
During Byleth's childhood, Jeralt shared little information about the world, the Church of Seiros and especially his past. Byleth either forgot or never learned their true birthdate, Jeralt claiming they were born years after the fire to a woman who supposedly died of illness. Jeralt trained Byleth in combat, eventually joining his band of mercenaries and gaining a fearsome reputation for their unflinching courage in battle. They would soon be known as the "Ashen Demon" as a result.
In recent times, Byleth has been having dreams of a young green-haired girl; however, when they inquire with Jeralt, he does not know anyone by the same description. Jeralt reminds Byleth that their next job will bring them to the Holy Kingdom of Faerghus, but a sudden uproar occurs when three students from the Officers Academy, Edelgard, Dimitri, and Claude approach the two, asking for their assistance with bandits who are trying to kill and plunder the trio. The three lords, with the aid of Byleth and Jeralt manage to dispatch most of the bandits when their leader Kostas attempts to kill Edelgard, spurring Byleth to take a blow for her. Just as Byleth is about to die, time freezes and Byleth encounters the green-haired girl once more who chastises them for being reckless. Introducing herself as Sothis, a name she just recalled. She and Byleth realize that they can rewind time to prevent Byleth's impending demise. The flow of time reverses, and Byleth is able to push Edelgard out of the way and disarm Kostas, quelling the remaining bandits.
Reinforcements arrive from the Knights of Seiros shortly afterwards and one of its members, Alois, recognizes Jeralt. He invites the two to visit Garreg Mach Monastery, and they comply. Before departing, Byleth converses with the trio from earlier, each impressed by their skill. They extend invitations to join the service of their respective kingdoms and Byleth expresses interest in one of them. Given the journey ahead, the trio get to know Byleth in order to sway them over to their side.
The Archbishop of the Church of Seiros, Rhea thanks Byleth for saving the students. Impressed by their skill, she hires them to become a professor of the students as a vacancy had just opened up. Despite Jeralt's wariness, Byleth accepts the position after Jeralt himself is asked to rejoin the Knights of Seiros. One of Byleth's fellow professors Hanneman asks Byleth to use his special device to determine if they hold a crest. To both their astonishment, not only does Byleth have a crest, but also it is a crest never seen before.
After taking time to talk to the three house leaders and learning more about the students in each of their houses, Byleth chooses one of them to serve as professor. This choice does not change much of the Academy Phase's storyline as the events of this phase are shared.
As part of their duties, Officer Academy students are given tasks each month by the Church. The first month, the Great Tree Moon has no formal mission for the students, just an annual house mock battle competition between the three houses. Through Byleth's leadership, their class emerges victorious. The Harpstring Moon marks the first formal mission that Byleth's class receives. Tasked with dispatching bandits at Zanado, the battle serves as the first real taste of combat to the students. This battle would mark the beginning of a long string of events behind a greater conspiracy.