Disgaea 4: A Promise Unforgotten yet, as it's set to come out in the States this September. But the game came out in Japan last February, and now Nippon Ichi has announced two different downloadable scenarios coming this August and October. The first is called "The Tyrant Valdorez," and will follow that character (along with his new playable moves) through a story with follower Fenrich. And the second is "Fuuka & Desco's Chapter Begins," focusing on the side story of those two characters.
Fuuka and Desco's story will also be available either in add-on disc form, along with a collectible Desco figurine, in a special edition Disgaea 4 collection with the full game, or simply as a downloadable content pack. Note that both of these DLC packs are only announced for Japan at this point -- it's unknown whether they'll see the light of day here in the US yet.