Elmer is a nine-year-old boy from Nevergreen City in the land of Popsicornia. Dressed in shorts, a striped t-shirt, a sailor's cap, and large rubber boots, he is a practical planner who carries a knapsack filled with supplies like rubber bands, a compass, and emergency lollipops. His empathy drives him to help the creatures he encounters, while his natural curiosity leads him to explore unknown places.

The Dragon is a young, flying creature originally from the mountains of Blueland. He features blue and yellow stripes, a red horn, red eyes, and gold-colored wings. Recently freed from his enslavement as a ferry boat, he is a gentle and trusting animal who wants to repay Elmer's kindness by flying him safely home.

Flute is a small canary who formerly lived as a pet in Popsicornia before escaping to Feather Island. She serves as a well-connected messenger for the island's community of escaped birds. Highly anxious and talkative, she worries constantly about an "island disease" of curiosity that is currently affecting her fellow canaries.

King Can XI is the royal canary who rules over Feather Island's bird community. As a descendant of the island's original human settlers' pets, he has inherited his royal position along with a heavy burden. He suffers from a sickness of intense curiosity regarding a long-kept family secret, which makes him grumpy, weak, and isolated.

Mrs. Elevator is Elmer's mother, living in the fictional city of Nevergreen. She wears long, old-fashioned dresses and keeps her hair in a neat bun. Though she initially disapproved of stray animals, she has grown to accept a stray cat into her formal home.

Mr. Elevator is Elmer's father, residing in Nevergreen City. He dresses formally in a suit and bow-tie. He shares a close, loving relationship with his family and has an upcoming birthday that motivates Elmer's quick return.

The Alley Cat is an old, striped tabby who formerly lived on the streets before being welcomed into the Elevator family's home. Well-traveled and knowledgeable, she previously provided Elmer with the crucial information he needed to locate the captive baby dragon.

Queen Can is a royal canary on Feather Island. She acts as a protective gatekeeper for her husband, managing his visitors and guarding his privacy while he suffers from his debilitating curiosity.