“The castle that everyone called home was no safe place for infants. Where could newborns be hidden in such dangerous times? The answer was in the Deeprealms- tiny worlds strewn across the astral plane. In the blink of an eye, babies grew into children. Soon after, to adulthood!”
The Deeprealms (秘境 Hikyō, lit. Secluded Realm) are a series of locations in Fire Emblem Fates
The Deeprealms are a series of areas in the astral plane in a similar fashion to the Outrealms. With the war between Hoshido and Nohr causing many hardships in regards to raising an infant, most of them are sent to them in hopes of keeping them safe. However, due to the accelerated time flow of the Deeprealms, infants raised in them quickly mature into young adults in a matter of weeks. All children of Fates are raised in these realms with their parents visiting them when they can. Each realm features a large enough area to raise them and the children usually have caretakers to raise them while their parents are off at war. However, these realms are not entirely safe as they are sometimes attacked by outsiders. Usually after a specific event in their young adult lives, the children leave their Deeprealm either by their parents' suggestion or their own begging, they end up leaving for various reasons, or show that they can fight.