It's called Disgaea Infinite, with NIS America explaining the story as such:

Laharl was almost assassinated, so of course he was MAD! Laharl and Etna ordered a Prinny to find out who tried to kill Laharl. The Prinny came across this awesome clock, which lets the Prinny (you) take over other characters' minds and bodies to discover who the unsuccessful assassin was. As the Prinny, you must collect hints and clues for the suspect...or the Prinny will get no salary...

"Adventure novel games are not as common here in the west, but it is a popular game style in Japan," the company added in its announcement. "Nippon Ichi Software has been publishing a variety of these games and Disgaea Infinite will be the first to make it over. The game will be packed with mystery solving and comedy for great laughs."