Unlock Pete
     This  is  only for Powerstone 1. Pete Beat the game once with any
character.

Unlock Weapons
     Complete  the  game  a certain number of times to unlock new, PSP
specific weapons:

Amenomurakumo:          Beat Game Five Times
Crystal Ball:           Beat Game Three Times
Decoy Bomb:             Beat Game Six Times
Giant Boots:            Beat Game Seven Times
Manches Chainsaw:       Beat Game Eight Times
Soccer Ball:            Beat Game Twice
Stone Sweeper           Beat the game with Julia
Totem Hammer:           Beat Game Nine Times
Twin Potion:            Beat Game Four Times
Thunderbolt Rider:      Beat the game with Accel
Turbo Helmet:           Beat the game with Pete
Wok Gun:                Beat the game with Gourmand

Unlock Bosses - Power Stone One
Final Form Valgas:      Complete the game with Valgas
Kraken:                 Complete the game with all characters 
                        (Except PS2 Characters)
Valgas:                 Complete the game with Kraken

Unlock Original Special Weapons From PS1
     Complete  the  game  once  with  any  character to unlock all the
original secret weapons from Power Stone one.

Machine Gun:            Beat Game Once 
Nyoi-Bo:                Beat Game Once 
Power Shield:           Beat Game Once 
Ray Gun:                Beat Game Once 

Unlock the two '???' mini games
     In the Power Stone Collection Menu there is one mini game already
unlocked.  By  obtaining  enough medals in a mini game, you can unlock
the other games.

Ayame's Shuriken mini game: Obtain at least 500 medals 
     Gunrock's Slot mini game: Obtain at least 1000 medals

Unlockable Characters
     Note: This is only for Power Stone 1:

Accel:                       Beat the game with Gourmond.
Gourmond:                    Beat the Game with Julia.
Julia:                       Beat the Game with Pete.
Pete:                        Beat the game once with any character.

Unlockable Characters in Powerstone 2
     Finish  1  on 3 Mode using the following characters to unlock the
extra characters for use in Power Stone 2:

Kraken:                      Beat the game as Falcon in 1 vs. 3 mode 
Mel:                         Finish 1 on 3 mode with Pride.
Pride & Kraken:              Finish 1on 3 mode with Falcon.
Valgas:                      Finish 1 on 3 mode with Kraken.