From the Shrine in Bitter Lake's North Shore, turn left and follow the beach line. Then go through the gate and continue going forward. You will run into a Treasure Hunter who is attacked by three Apramana Bats. Defeat them to save him and talk to him. Next you will find the Treasure Hunter in Valley of Ecstasy's Towers of Karma. From the Shrine turn back and go straight. He will be close and sitting on a tree. He is freezing and you need to use Ring of Fire in front of him to activate a cutscene in him warming up. Talk to him. Next head from Valley of Ecstasy's Brook of Bliss, turn left and drop on the right side of the bridge. Continue down the river and at the end, you can go do on the right side. Follow the path down and you will reach Melon Field Shrine at the bottom. Now just head into the big cave and Green-Capped Martialist will be there.