Nintendo and Atlus announced a crossover project called Shin Megami Tensei X Fire Emblem, the game will feature characters from both series. This will be one of the first collaboration projects between Nintendo and its partners.
http://www.youtube.com/watch?v=OK5-EIzDtKo&feature=player_embedded
http://www.youtube.com/watch?v=OK5-EIzDtKo&feature=player_embedded