Loading screen demon fangs trick
There are two loading screens in Okami:
The first one is a trail of paw prints followed by a picture of Issun, you can make the paw prints bigger by pressing X a little bit before they appear.
The second is a screen where pressing X multiple times will place a number of paw prints on the screen.

On particularly long loading sessions one can attain demon fangs. By carefully pressing X on the "trail" loading screen all the way through where you would normally see Issun, you will see big paw prints and a demon fang. The second type press X as fast as you can until you see a demon fang. Each time you do this correctly those demon fangs will be added to your inventory.

New Game
After the end of the credits at the end of the game, you are asked to save for a new game. All weapons except the 5th of each type transfer over. Peace Bell, Lucky Cat, Wood Mat, and Ink Pot are the only Holy Artifacts that transfer over. Brush techniques do not transfer over. Stats do transfer over.