In the movie, Audrey is a teenage girl while the Once-ler is an old man. However, many fans like to have her interact with the younger version of the Once-ler, either through time travel or an alternate universe. In this case, the two can be paired up romantically.
Usually, Audrey and the Once-ler are shown to be butting heads, as Audrey loves trees and nature while the Once-ler wants to chop down the forest. A popular scenario for the pairing is for Audrey to meet the pre-success Once-ler and become his friend while falling for his charm, and eventually having to stop him form destroying the forest. Whether or not she succeeds varies from story to story. Another popular idea is to make Audrey the leader of a protest movement against the Once-ler's company.
Outside the issue about the trees, most people think that Audrey would simply love the Once-ler's personality and talent. She would probably enjoy playing with him and the forest animals and would often listen to the Once-ler sing, while he may admire her artistic skill and caring nature.
Within the RotBTD context, this pairing is often seen in Modern AU stories, normally as a side pairing
Note: Please add only ones that are part of the RotBTD fandom
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