The World Ends With You Codes -

View total play-time:
Hold + at the save data menu screen.

Completion bonuses:
Successfully complete the game to unlock the following bonuses.

You can start a new session with your cleared saved game file with most of your previously obtained items and skills.
There is now an option to select any chapter to replay with bonus objectives at your cellphone menu.
You can now select A New Day Chapter and go to Shiba-Q Headquarters. At the third floor you can purchase the Ultimate difficulty as a quest item.
The "Another Day" chapter will now appear at the chapter selection menu. 

Hard difficulty:
Successfully complete the game under the Normal difficulty setting.

Alternate ending sequence:
Collect all of the secret reports, including the one in Another Day, to view a bonus scene after defeating the final Boss in the main story.

Save game file icons:
Complete the indicated task to unlock the corresponding character icon at the saved game screen.

Mr. Mew: Get 100% Pin Mastery. 
Rhyme: Collect all items. 
Rhyme (noise form): Complete the noise list. 
Beat: Complete the third week. 
Shiki: Complete the first week. 
Joshua: Complete the second week. 
Rhyme: Collect all items. 
Mr. Hanekoma: Collect all secret reports.