Amazon Japan posted a handy chart that shows all of the major characters from Final Fantasy IV and how they developed ten years later in Final Fantasy IV: The After Years.
The Kingdom of Baron has a few new faces like Luca, the daughter of King Giott who is working under Cid as an apprentice, and most notably Cecil’s son Ceodore. Yang also has a child. His daughter Ursula is the princess of Fabul. While Porom is a leader in Mystdia, Palom left his home (i.e. he’s not in the orange circle) with Leonora, a magic user from the Earth Crystal kingdom of Troia. No kingdom has as many new characters as Eblan. Edge, now the land’s king, travels with a group of ninja known as the Eblan Four. During the intervening years, Damcyan was rebuilt and Edward rules the land along with his secretary Harley.
Final Fantasy IV: The Complete Collection has a new scenario called the "Interlude" which covers the time gap between the two games.
Square Enix has Final Fantasy IV: The Complete Collection slated for April 19 in North America.