A Trekker's Charm is a sidequest you can pick up in Star Ocean: The Divine Force at the Village Of Eda.
This quest only becomes available once you have completed:
You can find Still Undaunted Explorer at the entrance of the Village Of Eda. He asks you to find a Scent Bag, which can only be gotten from the tail of a demon.
To complete this quest, you must destory the body part of an Ancient Chimera. You can find one at the beginning of the Hallowed Mount Galca-Lemthas area. Attack it's tail to receive a Scent Bag.
Once obtained, head back to Still Undaunted Explorer at the entrance of the Village Of Eda for your rewards.
Reward: