Location: Jinli Village
Petitioner: Fisherman
Reward: Mystery Chests, 3,000 coins / 5,000 coins

The most difficult party of this side quest is finding its location, Jinli Village, in the first place. Jinli is located far in the south of the map, and is accessible early on in the game - assuming you wander around a lot. Check the east side of Jinli to find a fishing pond, along with the Fisherman who will give you the quest.

Yi will beg the Fisherman to teach him the ways of fishing. The Fisherman will do so if Yi brings him one of each of the following fish:
  • Perch - Can be caught at Lotus Lake, a small dungeon area to the south of Luo Village, and east of Wild Boar Woods; the fishing spot is on the left side of the lake
  • Catfish - Can be caught in Jinli Village's pond
  • Sturgeon - Can be caught in Tianming Village, located southeast of Jinli Village, just past Tancheng City; the fishing spot is in the far south of the town
(If you're having trouble finding these places I recommend moving around on the World Map with the Map function. Default key is M, and you can move your mouse cursor to the sides to scroll. This is much faster than walking and hoping for the best.)

Bring the three fish back to the Fisherman and he'll give you your reward. He'll also immediately start up a new quest, Fishing Elder Golden Carp, and will demand you catch him a Golden Carp. You can grab one of these at this very fishing hole, so you might as well park yourself by the Fisherman until you nab one. Hand it over to receive your reward, which has... nothing to do with the secrets of fishing, but, hey. Money is nice.