1. Be sure to catch Lu Bu and buy 10 evocation pills.
2. Talk to Lu Lingfu in Yangzhou, and then there is a fake painting halberd behind Lu Lingfu.
3. Put this fake Tian Fang painting halberd on Lu Bu's equipment, and then talk to Lu Lingqi to trigger the task of Tian Fang painting halberd.
There is a wall at the top of the cave on the left, which is a bat cave. When you ascend to the throne, you will draw a halberd for Tian Fang after the Bat King kills you.