Icarus is a flying squirrel and the sole companion from the real world accompanying Nemo into Slumberland. He communicates using squirrel vocalizations mixed with broken English, delivered in a distinctively high-pitched, screechy tone. This voice physically pains the friendly Boomps of Nightmare Land, leading Icarus to consciously lower his volume around them. He demonstrates unwavering loyalty to Nemo, rarely leaving his side during their adventures. This devotion drives him to confront any perceived threat to Nemo or their allies, regardless of danger. His initial interactions with Princess Camille are tense after she mistakes him for a rodent, an error he strongly objects to, though their relationship gradually improves. Icarus shares Nemo's fondness for sweets, particularly enjoying cookies given by Princess Camille, and readily consumes human food. He actively participates in critical events alongside Nemo, including the journey to Nightmare Land and the final confrontation with the Nightmare King, providing support during the climactic battle.