Kingdom Hearts: 358/2 Days:

Unlockables
King Mickey in mission mode: Finish story mode
New Game +: Finish Story Mode once in any difficulty.
Play as Donald and Goofy in Mission Mode: Beat Story Mode once in any difficulty
Play as Xion in Mission Mode: Beat Story Mode once in any difficulty
Sora in mission mode: Finish story mode
Goofy: Play story mode to day 277
Riku: Play story mode to day 171

Theater Mode
Beat the game once, and Theater Mode will become available to you. You'll be able to watch every cutscene in the game.

New Game +
Finish Story Mode once in any difficulty using any character.
New Game +: Finish Story Mode once in any difficulty using any character.


Unlocking Characters in Mission Mode
Donald: Play story mode to day 244
Goofy: Play story mode to day 277
King Mickey: Beat the game and purchase the item Return of the King from the moogle shop
Riku: Play story mode to day 171
Sora: 100% complete all missions and purchase the item Soul of Sora from the moogle shop
Xion: Play story mode to day 96