In order to trigger this quest you must complete the Gusu City quest Husband Material. This will allow you to Invite Lü Xian'er into your party. Once that's done Xian'er will express her desire to travel to Pingyang Fortress, which technically triggers Four Martial Arts Families...
... but you won't be able to actually do this quest until much later in Wandering Sword. Pingyang Fortress is located in the northwest of the world map, where the landscape becomes autumnal, and your passage into this area is blocked by the guards in Fancheng City. You won't be able to travel to Pingyang Fortress until you've completed the main story quest Prepare Birthday Gift. Once that's done you can cross the border, and you'll find Pingyang Fortress to the north of Fancheng City.
Assuming Xian'er is in your party, you'll be forced into a friendly Sparring match the second you set foot in Pingyang Fortress.
Wang Tiancong
This fight is fairly easy, despite Wang Tiancong's high HP. All of his attacks are quite basic polearm techniques, and their AOE reach doesn't matter much against a single opponent. The one exception is Phoenix's Talon, which does have substantial reach - but doesn't hit all that hard. Get in close and clobber him with Xian'er's spear.
You don't have to win this fight, though if you do you'll receive the Vedas Polearm Technique manual, an Exorcism Staff, and another random piece of equipment.
Tiancong's father, Wang Daoming will show up and ruin the meeting, sending the son off to brood elsewhere. Xian'er decides to follow him. There are two things to grab before you leave:
- Check up the ramp next to the fortress' entrance to find a chest containing a Demon Conqueror, Martial Arts Thoughts, and Zhennan Wood.
- To the east you'll find the father watching over some trainees. Look to the left of Wang Daoming for a chest containing a Note of Whim and Improvisation and a Geng Metal Pill.
- Also to the east you'll see a horse attached to a wagon. The wagon has a chest on the back that you can't open, but if you look behind the chest you'll find a smaller, hidden chest. Check this second chest for Two-Time Refined Spirit Pills, Gougi, and Tanxiang.
