The Precious

Speak with Isamu in Sunstream City (194, 88).

Pay 15 Gold to Isamu in exchange for the information he possesses.

Travel to the Bamboo Peak in Jadeon and search the mound of rocks (-400, 150) for anything out of the ordinary.

Isamu lied! Return to Sunstream City and confront him.

Having confessed that he had also been tricked, travel to the Crystal Hall in Jadeon and speak with Metaphysician Yass (66, 112).

Yass claims that the information he provided Isamu was correct. To prove it, he requests that you kill 18 Monkey Phantasms in the Jadeon wilderness (230, -140).