Location: Pingyang Fortress
Prerequisite: Complete Four Martial Arts Families
Petitioner: Wang Daoming
Reward: None - but see below
In order to trigger this side quest you first need to complete most of Lü Xian'er's storyline, up to and including the Four Martial Arts Families side quest. Return to Pingyang Fortress, in the northeast of the world map's northwestern region, and speak to Wang Daoming, the castellan, to begin the quest.
Daoming expresses concern over his son, Tiancong, who has lost faith in his martial skills. Daoming wants Yi to gather enough Coldiron Ore to forge Tiancong a new weapon. He needs Yi to find the ore. Coldiron Ore shows up fairly often as you're exploring outdoor areas, and the closest place you can find it is on Mount Autumnscape, to the west of Pingyang Fortress. Three pieces of Coldiron Ore will do.
Travel back to Pingyang Fortress and give the ore to Daoming. He'll exchange them for a Phoenix Cry Staff. Take this to Tiancong, who is standing to the southwest. This will end the side quest, sending Tiancong out of the fortress and over to the Xungu Pass. You won't receive a reward for completing this quest - but Daoming will owe Yi a favor, which you can turn in during another, longer side quest, Sweet and Bitter Springs.