Start from the twin's house. Go down the ramp and talk to the old lady on it. Talk to the energetic man and the two women by the well. They all have nice stuff to give you. Head to the ramp's start and take a left through a tunnel. Follow the path into the cave. Throughout the cave, always take the path that looks like it leads to higher ground. When you keep going and hit a door that says, "I demand an offering of black wings... and poisonous... fangs," go back. Take out the first bat and hold and press . Let go of and press again to do Penguin Parade. Lead the viper to the door. You might have to re-penguin him, because it wears off. Talk to the door and it accepts the viper. Go back and repeat the step, except to the bat standing there.
Throughout the cave, keep the tactic on Save MP so they have a lot of MP to kill and heal with during the fight behind the door. Remember to equip that sword that your twin gave you. When you get in there and watch the cutscene, stay back and cast Volt with the little boy Rico and try not to get hit by the fireball. Before the fight, put them on Spread Out. Rarely attack the ogre yourself, but use them as a weapon. Keep your distance and keep fighting the ogre until he falls. It turns out that the dragon on the stand was being controlled by the ogre. He gives you something to heal Aya with and two more flutes. It costs MP, but restricts magic damage done to allies in the range of the flute. The other allows hidden things to be seen and or removed.
Go behind the dragon's stand and use the flute that allows objects to be seen and or removed, and play it. The wall directly behind the dragon will disappear. Go down the stairs and follow the path and look to the right behind the first pile of rubble. You will see a red chest, so open it and you will find a nice surprise. Continue following the path and head out the door at the end of it. Go back to the twin's house and a cutscene will begin.