One of the big secrets of the game is that Princess Garnet's true name is engraved on the Eidolon Wall at Madain Sari. There is a very complicated way to reveal the truth at the beginning

First, form a party with Dagger and visit Lani who is standing on Eiko's back porch. Upon arriving Lani will run away. Exit the village and return with anyone except Dagger or Amarant and talk to Lani twice. Exit the village and return with anyone except Dagger or Amarant and talk to Lani twice. Read the message and go to the Eidolon Wall. Walk clockwise from the entrance (heading to the right) until you return to the entrance. Move just past the "!" until you hear a chime. Then walk counterclockwise back to the entrance, just past the "!" again. Repeat this 9 times, going back and forth. Make sure you hear a chime each time. On the ninth round, your HP/MP will be recovered and all status abnormalities removed.

Now read the paintings. You can read them in any order, as long as you read them all. A whole slew of extra messages appear this time. At the end, return to the Ifrit drawing and look for an extra message, revealing Dagger's true name.