Information about how to recruit Seteth in Fire Emblem Three Hopes.
In Fire Emblem Three Houses you could recruit many characters simply by getting specific stats and skills high enough. Once done, they’d be impressed enough to realize that studying under you would suit them better than petty considerations such as life-long friendships, national loyalty, familial duty or even religious conviction.
Unfortunately characters in Fire Emblem Three Hopes aren’t quite as malleable - some characters will join your faction as you progress the Main Questline, usually due to story contrivances entirely outside of your control. The rest, however, must be met in battle and “persuaded” to join you… often by lumping them on the head enough times to realize that they’d be better off defecting than decomposing.
Character Recruitment Strategies
In the case where a character can be persuaded to join you, this “persuasion” effort is achieved via the deployment of a Strategy. When you start a battle in which a character can be recruited you’ll first have to pick from a variety of available [Strategies]. You can find more information about Strategies on their own page, but for the purposes of recruiting characters you’ll be interested in any “Persuade [Character]” Strategies, which you must select prior to the battle to ensure you can utilize said Strategy(ies) during the battle. Deploying Strategies in turn require you to expend Strategy Resources, a currency gained by completing [Side Quests] during the chapter leading up to the Main Quest where enemy characters can be recruited.
During battle, when the character you wish to recruit spawns you must activate the Strategy to persuade them by entering the battle menu before you defeat them. If you defeat them without activating the Strategy - even if you selected it before the battle - they will die and you will not be able to recruit that character for the rest of the playthrough! Once the Strategy has been activated, the area where the Strategy is in effect (usually where the target character spawned) will be surrounded by a purple glow. Merely defeat them in this area and you’ll recruit the character.
How to Recruit Seteth in the Scarlet Blaze Route
How to Recruit Seteth in the Azure Gleam Route
Seteth and Flayn join Rhea and the rest of the Church of Seiros in seeking sanctuary in the Kingdom of Faerghus. During the Main Quest battle at the end of [Chapter 4], escort Rhea to the center of the map (past where you encounter and can recruit Hapi), after which she’ll ask you to assist Seteth and Catherine, who will spawn in the northwestern and southeastern corners of the map, respectively. Keep these two alive by defeating the enemies around them, then push some boulders to block the flow of some lava to provide them with an escape route. Ensure the way ahead of them is clear and they’ll rendezvous with Rhea, assisting you as you defeat Petra (who can also be recruited) along the northeastern end of the map. Finally defeat Hubert to finish the mission.
Seteth (and Flayn) will join you at the start of [Chapter 5].
How to Recruit Seteth in the Golden Wildfire Route