Gregal

Quote from The Legend of Zelda: The Minish Cap Gregal & the Ghost figurine:

"An old man plagued by an evil spirit. Coming to his aid will bring you benefit in the end, so if you meet him, you must find a way to help him."

The only way to save Gregal is to fuse kinstones with the young man of the Wind Tribe that is found inside a house of Hyrule Town. This will create a portal to the Cloud Tops, where you can find Gregal and help him by sucking the spirit with the Gust Jar. Be sure to find him quickly, because if you wait until you already finished the Cave of Flames he will not appear. He rewards you by upgrading your arrows to Light Arrows.