Location: Wutong Village
Petitioner: Sun the Physician
Prerequisite: Complete Cave Fight
Reward: Varies; see below

Yet another side quest that doesn't unlock until you've reached the more open-world sections of Wandering Sword,      appears in Wutong Village once you've traveled into the Cave in the Mountain. Once everything inside there is finished you can speak with Sun, Wutong's doctor, to begin the side quest. He lives on the west side of the village.

Sun is a regretful man, and he'll talk about how he hasn't visited his home, Nanjiang, in a long time. You have two potential responses to Sun's problem.

You are pretty open-minded

Choose this option and Sun will philosphize a bit longer. He'll then give you an Azure Flower, and ask you to pass it on to Dachui the Blacksmith. You'll find Dachui's smithy to the south of Sun's home. Dachui will give you 600 coins, ending the quest.

Why not go back while you're hale

If you suggest Sun return to his home for a visit he will spurn the idea, as he's too old. He will, however, make a request: Bring him a Begonia from Nanjiang. He'll give you a Xin Metal Pill, a Yi Wood Pill, and Martial Arts Notes as a reward. This will end the side quest...

... but the request for a Begonia will remain. (We'll have to come back to this. You can explore a bunch of the world map at this point, but as far as I can tell you can't reach Nanjiang until you've gotten further in the game. I couldn't even find it while I was scrolling around. I'll edit this section once I've gotten a Begonia.)