Nippon Ichi's support for the DS will be continuing beyond Disgaea, Jigsaw World, and The Convenience Store DS. The latest DS announcement from the Japanese parent company of NIS is Marl Oukoku no Ningyouhime, presumably a new entry in the series that came to the US PlayStation under the name Rhapsody.
The company unveiled the new title through a teaser website that lists its genre as "musical RPG" and promises a Japanese release date of August 7.
That's all we know at the moment. The site will see its full opening on June 6, but for now browse on over there for some attractive artwork.