The player takes on the role of a Prinny who is commanded to investigate the attempted "assassination" of overlord Laharl. Disgaea Infinite starts with a travel back into time where the main character will possess other characters to obtain information and gather clues to solve the mysteries.
The game takes place in the Netherworld from Disgaea: Hour of Darkness. As such, several important characters from that realm appear in the game, including Laharl, Etna, Flonne, Prinnies (and the main character Prinny), Jennifer, Captain Gordon, and Thursday. The game also features Mao and Raspberyl from Disgaea 3 as major characters. Asagi also makes a minor appearance in the game's bonus ending.
The game begins with the main character, Prinny, meeting up with Etna, Flonne, and Laharl. Laharl is looking for the Super Rare Pudding that he believes Etna is hiding. While cleaning Laharl's bedroom, he finds a watch item, which is later revealed to be Tick Tock.