This quest is available starting in Chapter 7.
In seek mode, look for the boy that's on top of the Dye Shop searching for something. Go behind the color shop via a narrow pathway to the right. Climb the ladder and talk to the boy. The boy will tell you to talk to the Fortune Teller to look for his lost cat, Mari. Do so, and she will tell you to follow a cat in Fountain Plaza. Go to Fountain Plaza and follow the cat into narrow areas. After finding the cat, talk to the boy again.