New Game +
     Go through the main game once to unlock New Game Plus.
     
Unlockable:                   How to Unlock:

New Game +                    Finish the game once.


Ultimate Weapons
     Available only in a 2nd playthrough or more, Death will sometimes
hide  within  treasure chests. Chests containing Death will prompt you
to pick between the choices to open or ignore the chest. If you choose
to  open the chest, you will have to fight Death, which when defeated,
will drop the ultimate weapons for the characters.

Unlockable:                   How to Unlock:

Ultimate Weapons              Defeat Death.


Secret Weapons
     By  returning to completed dungeons, you can find the characters'
secret weapons. Note: No secret weapon available for Chie.

Unlockable:                   How to Unlock:

Main Character's secret 
weapon                        Defeat extra boss in Void Quest.

Yousuke's secret weapon       Find in boss' den in Mysterious 
                              Shopping Street.
                              
Yukiko's secret weapon        Defeat extra boss in Yukiko's Castle.

Kanji's secret weapon         Defeat extra boss in Steamy Bath House.

Kuma's secret weapon          Defeat extra boss in Opera House.

Naoto's secret weapon         Defeat extra boss in Secret Lab.