Special Delivery
Requirements
Speak to Finley and accept the quest to begin.
Walkthrough
The idea here is to follow and protect the letter container until it gets to the end of its journey. Mostly this just involves patience.
The first time interaction is required is when the container reaches a wooden barrier. Pick it up and throw it over.
Now move ahead of the letter carrier slightly and throw a bomb into the water a bit ahead of it. Be very sure the bomb is not close to the carrier or it will destroy it. Follow bomb and carrier down the river, detonating the bomb when it gets close to enemies or barriers and throwing another to replace as needed. There should be only one more barrier, and enemies mainly tend to ignore the container and focus on you instead.
When the container finally reaches the end of its journey, approach to trigger a cutscene.
Set the quest as the active marker (if it is not already) and head back to Zora's Domain to head to the marker and complete the quest. The reward is a gold rupee.