Opal is a character who is found throughout the game outside the hotel in Folsense. Opal seems to be depressed about the town going into decline and various other events that have happened in her life. Professor Layton and Luke Triton brew her some Tea to help her feel better.
Opal wears a yellow dress and has a distinct haircut.
Opal gives the following puzzles in Professor Layton and the Diabolical Box:
"One of the few remaining members of Folsense's aristocracy, Opal lives in the lap of luxury on the north of town with her husband. She secretly dreams of having a simpler life, which is why she sewed her favorite yellow dress herself."