To unlock the characters below, fulfill the corresponding requirement.

Asagi - Clear Extra Map #4
Axel - Clear Extra Map #4
Etna - Clear Extra Map #7
Flonne - Clear Extra Map #7
Laharl - Clear Extra Map #7
Marona - Clear Extra Map #5
Master Big Star - Clear Extra Map #1
Prism Red - Complete Extra Map #3
Salvatore - Complete Extra Map #2