Here is the full list of all 30 Disgaea PC achievements.
Completed Final Episode of Etna Mode "Chronicles of Etnarnia"
Defeated all EX bosses!
Defeated the Extra Boss "Item God 2"
Obtained the Hyperdrive!
Defeated the Extra Boss "Item God"
Completed Ep. 1 of Etna Mode "Super Dimensional Etna"
Defeated the Extra Boss "Item King"
Performed 10 transmigrations
Obtained the Dream Hand!
Defeated the Extra Boss "Baal"
Dealt 10,000,000 Damage!
Defeated the Extra Boss "Marjoly"
Cleared Extra Stages "Cave of Ordeal"
Defeated the Extra Boss "Priere"
Obtained 10,000,000 HL at the end of battle
Obtained Total LV 10,000
Dealt 100,000 Damage!
Obtained Total LV 5,000
Obtained Total LV 1,000
Completed Final Episode "What Lies Beyond the Battle"
Obtained Total LV 100
Completed Ep. 10 "Angels, Demons, and Humans"
Killed 1,000 enemies!
Obtained 1,000,000 HL
Completed Ep. 5 "Etna's Secret"
Killed 500 enemies!
Performed your first transmigration
Defeated the Extra Boss "Item General"
Killed 100 enemies!
Completed Ep. 1 "Prince of the Netherworld"