Ghost Buster Request is a quest that is available after the thugs have been cleared out of Hermit's Nest.
The quest is initiated by talking to Lihong and Meiling, who are standing in the Sunflower Grove next to the platform used for sparring. The children inform Ryo that they have witnessed a ghost in the Abandoned Temple and want Ryo to help them remove it.
Ryo has to wait until after 7PM and visit the Abandoned Temple, and speak to Mr Sun, who is sat on the ofrertory box. When Ryo speaks to Mr Sun, he advises that the children are mistaken and the ghost is simply him gathering Moonlight Mushrooms for food.
Ryo has to search within the area of the abandoned temple to find all of the Moonlight Mushrooms. Once he has collected them all, he returns to Mr Sun and Mr Sun tells him he is done talking with him
Ryo returns back to Lihong and Meiling in the Sunflower Grove, asking them to leave the Abandoned Temple alone, and the children give him a reward.