You cannot access DLC immediately. You must progress through the main story first:
: After finishing the "Two Chasms" map, the Outrealm Gate (異界の門) will appear on the world map. Fire Emblem: Kakusei (DLC) [Decrypted] 3DS (JPN...
Since you are looking at a file for Fire Emblem: Kakusei (known in the West as Fire Emblem: Awakening ), 1. Preparation You cannot access DLC immediately
: Difficult story-based maps focused on the children characters. Preparation : Difficult story-based maps focused on the
: You must have the Japanese version of the base game ( Fire Emblem: Kakusei ) installed. DLC files are region-locked and will not work if you try to apply them to the North American or European versions of the game.
Open Citra and right-click on Fire Emblem: Kakusei in your game list. Select Copy your decrypted DLC folders/files into this directory.
Alternatively, go to File > Install CIA if your DLC is in .cia format (even if decrypted).