To unlock the dark sun stages you need to push various buttons located in Adell's village. There is a button located behind the square column behind the Post Office/Dark Assembly. Another is located behind Adell's house on the window after going down the little set of stairs. The third is located on the very bottom right hand corner off the map next to a tree in the corner near the ghost. The fourth is located in a break in the wall of the left where the Petite Orc is standing. The last button is located behind the house behind where the zombie is standing. It will be against the wall. Once you hit all five a message will appear saying "A Shadow has decsended upon Holt Village!" After that the guide Friday MKII will appear next to the tree where you hit the one switch.Talk to her five times she'll ask if you wish to accept her challenge, on the 6th time she'll ask again. Accept her challenge and defeat her (She is level 100)and she will then stand next to the dimension guide. Then you will need to fulfill various special conditions in the normal stages of the game to unlock it's dark sun counterpart.
Get Asagi (monster form) to level 2000 then pass her bill which will unlock her human form and you will lose the monster form however you can switch her back by passing the bill "I like monsters better" and you can switch her back and forth as long as you want.
Priere: Have Adell get 66+ Felonies to unlock her stage. Then beat her and pass her bill with Adell as a senator. You must unlock her stage anytime during Episode 1-9
Zetta: Beat 10 of the Dark Sun stages then pass Zetta's bill to unlock his stage. Beat him and pass his bill with Adell as a senator.
Mass Produced Kurtis: Summon the Defender of Earth 4 times using a cell phone, pass the bill to unlock the first stage then beat it. Then use the Cell phone again 4 times pass the Save the Defender of Earth bill again, beat the stage and Kurtis Copy will be unlocked.
Disgaea 1 Female Samurai: Have a save data from Disgea Afternoon of Darkness.
Asagi: Have Adell get 33+ felonies, Unlock Asagi's stage, beat her, then pass her bill with Adell as a senator.
Mr. Champloo: Unlock Mr. Champloo's stage with 50 hours or more of game play time and after completing Axel mode.
Flonne: Unlock her Stage with 40 hours or more of game play time. Then during Episodes 12-13, defeat Flonne.
Laharl: Unlock Flonne, then pass Flonne's bill With Adell as a senator then complete the stage.
Gordon: Pass Gordons bill with Adell as a senator after completing Unlocking Mass Produced Kurtis.
At the 'Start' screen place the cursor over 'New Game' and press Triangle, Square, O, Triangle, Square, O, X and you will begin a new game in Axel mode where the enemies are at reduced levels. Axel mode on the PSP has several gameplay features which are exclusive to the PSP platform and carry over to Normal mode when beaten.