Hunter & Prey (狩る者狩られる者 One Who Hunt Hunters in Japanese Version) is Paralogue 10 of Fire Emblem Fates.
This paralogue is unlocked when Kaden has obtained an S-Support with a female character.
The script for this paralogue can be found here.
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.
This map is a heavily dense forrest terrain, especially in the middle where Selkie is. Fortunately, there are no immediate threats to Selkie aside from a few scattered Snipers near her that cannot move and basically cannot attack her.
Selkie herself will move towards the northeastern part of the map, killing Snipers until she reaches Daichi. On Normal, she most likely will not get to Daichi until around turn 8, giving the player time to get to her and talk to her with Kaden. On Hard and Lunatic, especially if done later in the game, the snipers will most likely be too sturdy for her to kill in less than 3 turns, so there is a lot less stress towards approaching her.
After Selkie is recruited, the map becomes much easier and is relatively simple to complete. If planning on capturing Daichi, make sure to have Orochi or Niles to do so. Otherwise, clear the map and enjoy having access to Selkie.