Once-ler and Anna are both energetic, happy-go-lucky characters with big dreams, but are also quite naive. They would most likely bond instantly over their mutually happy and optimistic personalities, and many fans like to imagine them singing together and playing with the forest animals. As with Audler, Mavler, and Rapunzler, fans of the pairing believe that Anna would be (or attempt to be) the Once-ler's "voice of reason" when he is trying to decide whether or not to destroy the forest.
There are several theories as to how the two would meet, but since Anna is a princess, it is likely that she would not meet the Once-ler until after he becomes famous, most likely at some kind of high-class gathering such as a party (much like ThinIce).
In their formal/fancy clothes, Anna and the Once-ler also appear of have inverted green-and-black color schemes with contrasting themes; Anna's ball gown represents nature and flowers, while the Once-ler's suit represents money and greed.