The game is listed as as PSP emulation title, meaning that it will appear as part of the Classics Catalog for PlayStation Plus Premium subscribers.

A June 30 release date is listed, but given that it is July 19 and the game is not yet available, that release date is incorrect.

Here is an overview of the game, via western publisher NIS America:

About

Disgaea is now on the go! Enjoy your favorite miscreants on your ride to school, work, home, or wherever. Challenge your friends through the exclusive multiplayer mode, and prove beyond a doubt just who deserves to rule the Netherworld.

Disgaea: Afternoon of Darkness tells the story of Prince Laharl and his outlandish group of misfits as he battles for the ultimate rule over the Netherworld.

Key Features

• Remastered – Completely remastered to take full advantage of PlayStation Portable.
• Multiplayer Mode – Gratify your ego and humiliate your friends in the multiplayer mode.
• New Story Mode – Discover what would happen if Etna killed Laharl. All-new story focus means a new experience and an all-new ending.
• Fog of War Option – Less visibility, more strategy.
• Geo Cube – Outwit your friends with the Geo Cube. Geo Cubes can turn a battle in a moment. Use them well or have them used against you.

Thanks, @Renka_schedule.