In the above Fire Emblem: Kakusei image, there's a character named "Lightning". In Final Fantasy XIII, there's a character named "Lightning". Hey, wait a second...

This seems to be a player's My Unit creation—and one that really, really looks like Final Fantasy's Lightning.

Lightning appearing in Fire Emblem would make more sense than, say, Mass Effect outfits showing up in Final Fantasy.

3DS『ファイアーエムブレム覚醒』はライトニングさんそっくりのキャラも作れるのか [トー速]