Disgaea 3: Absence of Detention

Play for 10 hours straight. A lot of people have trouble with this for some reason. It's not 10 cumulative hours, it’s 10 hours straight. You can put the Vita to sleep and come back later. You can even go to the main Vita menu, browse trophies, etc as long as you don't actually close the game (done by pressing the PS button and swiping the corner down from the right) your time will keep adding towards the 10 hours.