——Dimitri Alexandre Blaiddyd
An Inevitable Encounter is the prologue of Fire Emblem Three Houses.
A great war which consumed Fódlan over a thousand years ago between the Great Liberation King and the holy figure Seiros lead to a decisive victory for the latter. Hailed as a hero, she would go on to establish the Church of Seiros.
In the present, Byleth, a young mercenary, has been having dreams of a mysterious green-haired girl. Their father, Jeralt, the leader of a band of mercenaries is unsure of whom Byleth is seeing in their dreams. While they are preparing to depart to the Holy Kingdom of Faerghus, their lodging is approached by some individuals seeking help from bandits. Rushing to their aid, the bandits are nearly defeated, however their leader prepares to assault one of them, forcing Byleth to intervene. However, just as they are about to take a mortal wound, time suddenly freezes. The green-haired girl, calling herself Sothis, has used her power to stop time and prevent Byleth's demise. By rewinding time, the scene replays with Byleth disarming Kostas and forcing him to flee.
Members of the Knights of Seiros arrive to assist in the rescue, but one of their leaders Alois is surprised that the bandits have already been dispatched. To his surprise, he sees Jeralt, his former captain for the Knights. Alois asks Jeralt to accompany him to Garreg Mach Monastery, much to his displeasure. The three youths, introducing themselves as Edelgard, Dimitri, and Claude, the future leaders of the three main nations of Fódlan, are impressed by their skill in the battle and use the traveling time to learn more about Byleth and hopefully sway them to provide their skills in service to their nations.
Subjective: The following part of this article is based upon the editor's personal experiences and opinions, and therefore may not be applicable for all readers.
The battle is relatively straightforward as you will need you simply defeat Kostas. The enemies are weak and should not pose too much issue for your deployed four characters.
It is important to note that EXP from this fight will carry over into the future chapters. While you are given four characters immediately, you will not be using two of them for the rest of the playthrough. While it may be early to decide for some, Byleth and one of the other three should secure the kills to maximize the EXP gained from defeating the bandits. Jeralt will also be there as an NPC, but on normal, he will likely not be needed to complete the map. On higher difficulties, he can either help end the map in a pinch or soften the enemy so Byleth and your desired character can gain the experience they need. The three other characters can talk to Byleth, granting some support points between the two, thus use it to get an early start establishing Byleth's support with them.