Once-ler and Honey Lemon both have optimistically sunny and energetic personalities. They are also both apparently smart, as Honey is a master chemist while Once-ler is an inventor. Fans believe that the two would get along exceptionally well, always feeding off of each other's energy. They would often encourage each other's different projects and possibly drive each other crazy as well. Some fans see this dynamic to be platonic, while others see it as romantic.
Additionally, both characters are quite tall and rather lanky, which leads several fans to think that they look cute together as well as having similarities.