In a semi-homage to Final Fantasy Tactics, FF IX includes a collection of twelve Zodiac Coins. The Coins are scattered about the world in various hidden places and appear in your Key Items list when collected. To receive your rewards for the coins, take them to Queen Stella's palace in Treno and talk to her assistant. Choose the first option to hand over your coins one at a time. (Note that the rewards you receive are dependent on the number of coins you've given to Stella, not which specific coins you give.)

   After you give Stella the twelfth Zodiac Coin, talk to her again and she'll ask you to find the thirteenth Coin. Choose the first option to accept the mission and Stella will give you all your Zodiac Coins back. If you examine them, you'll find a riddle -- "Who kissed Virgo?" -- as well as hints to its answer. The answer is "Scorpio", so head back to Quan's Dwelling and search the spot where you found the Scorpio Coin. You'll receive the thirteenth coin; it won't be there unless you've been sent by Stella, however. Once you've got it, take them all back to Stella and you'll be rewarded with Shina's hammer, the Tonbachi. And what would you want with a hammer? See the Hades sidequest for details.