Detached Princess (閉ざされし皇女, Tozasa re shi Ōji lit. The Closed Princess is the first Xenologue of Fire Emblem Heroes. Unlike most other chapters or paralogues in the game, this Xenologue only has a single part.
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.
Whether you move your units one block away from Ephraim's attack range or exactly on his attack range, he will move forward in the Enemy Phase. If one of your units is a powerful green melee unit, then you have the advantage and you'll take him down at ease.
Then if your blue melee unit goes into Chrom/Lucina's attack range, your unit will take them down easily. Your blue ranged unit can go into Leo/Elise's attack range and deal with them easily enough.