This works only in single player. Right before an enemy attack hits, quickly go into the menu (via touch screen if you're fighting) and you'll here the sound effects of the attack. But once you exit it, no damage was done and you can continue fighting. Note that you can still get hit if you exit the menu while the sound effects are still going on.
Attack the Napdragon at the start of the game. The dragon will not take damage or fight back. You can easily gain Weapon skill experience without any danger.
Note: Origin Island required. After completing the main quest line Pam will begin to have a visitor. This visitor is the Exchange Clerk who trades Golden Lunares Coins for items. Pam will also begin to take requests. The reward for each request will be 2 Silver Lunares Coins. 4 Silver Lunares Coins can be exchanged for 1 Golden Lunares Coin by the old man. The old man can be found next to the Goddes Statue in the Rocky Hill Shrine area.
To enter a password, go to the Post Office and talk to Aikotoba-san. When entering the password, characters in lowercase are hiragana, characters in all caps are katakana, and characters within brackets are small characters.