Obtained from the bulletin board in the fishing village, this side-quest has you gathering Poisonous Herbs.
This is a simple fetch and scrounge quest that requires you to obtain x10 Wolf's Bane that can then be used to upgrade weapons making them poisonous.
The area where you can obtain this is clearly marked on the map - you are looking for purple-tipped flowers - Wolf's Bane in other words... The game may suggest that you look along the western edge of the map - but that is bad advice. You will find them in the southeast section - look for the markers on the map.
The river/stream bed there is loaded with them!
Once you have the ten you need head back to the Fishing Village and speak with Musa to get your reward.