New Game+ Feature
After the end of the credits at the end of the game, you will be asked to create a save for a new game. All weapons except the 5th of each type will transfer over, however Peace Bell, Lucky Cat, Wood Mat, and Ink Pot are the only Holy Artifacts that transfer over. Brush techniques do not transfer over, but stats will transfer over.
Unlock the Okami Jukebox
Complete the game once to unlock the Okami Jukebox.
Loading Screens Trick
You can attain demon fangs to add to your inventory in the game by manipulating the loading screens. There are two in the game, one with a trail of paw prints followed by a picture of Issun, and by pressing X right before they appear. During long loading sessions, by carefully timing all these button presses all the way through, you will attain additional demon fangs which will be added to your inventory in the game.
When you finish the game, you have to complete the game a certain way in order to open most of these codes.
Invincibility - Pick up every Stray Bead. There are 100.
Secret Theatre - Play for over 31 hours.
Kamic Returner - Finish the game.
Stray Bead - Finish the game.
Kamic Transfomer 9 - S-Rating for "Praise Earned"
Kamic Transfomer 8 - S-Rating for "Praise Earned"
Kamic Transfomer 6 - S-Rating for "Demon Fangs Found"
Kamic Transfomer 7 - S-Rating for "Praise Earned"
Kamic Transfomer 5 - S-Rating for "Money Gained"
Kamic Transfomer 4 - S-Rating for "Enemies Defeated"
Kamic Transfomer 3 - S-Rating for "Deaths"
Kamic Transfomer 1 - Finish the game.
Kamic Transfomer 2 - Finish the game.