Duplicate quest rewards:
     Complete  a  quest,  then  speak  with Wind to bring up the quest
menu.  Press  A, A. When you hear the sound of a chime, press Start to
quit  from the quest menu. You will now have the quest reward, and the
quest  should  still  be  uncleared  from the list. Complete the quest
again to get the reward again. You can repeat this trick as many times
you want.

Birthday cake from Vincent:
     Change  your  birthday  in the Nintendo DS system settings to the
current  date.  Then,  go  to the shopkeeper. VIncent will offer you a
birthday cake for 3,000.

Secret Vincent dialogue:
     Play  as  Charlotte and stand in front of Vincent the shopkeeper.
Hold Up until he begins speaking.

Enable English voiceovers:
     To  enable English voiceovers in Japanese version of the game, go
to  the  main  menu,  hold  L  and  press  A. If the code is accepted,
Jonathan will say "showtime".

Unlock Old Axe Armor as playable character:
     Kill at least 1,000 Old Axe Armors and save the game then start a
new game. Now you can select Old Axe Armor to play.

Finisher bonuses:
     Complete  the  game  with  the  best  ending  to  unlock  the the
following bonuses:

- Hard difficulty level
- Boss Rush Courses 2 
- Boss Rush Courses 3
- Richiter and Sisters mode (start a new game with a different duo) 
- Sound mode 
- New Game+.