The Gray Heron is a central figure in the story, serving as both an obstacle and a guide for the protagonist. Initially appearing as a large, mysterious bird that frequents the estate, this creature is later revealed to be a supernatural entity: a short, bald, and pudgy man who resides within the heron's skin and operates its form like a puppet. This being is defined by its trickster nature, weaving together a complex personality that is at once threatening, comedic, and, eventually, loyal. Its primary motivation is ambiguous for much of the narrative, as it lures the protagonist with the deceptive promise of reuniting him with his deceased mother, using this bait to draw him into the magical world connected to the mysterious tower. However, its actions are ultimately revealed to be in service to the tower's enigmatic master, who commands the heron to act as a guide.

Within the story, the Gray Heron plays an indispensable role as a guide and a catalyst for the protagonist's journey. It is the heron's taunts and claims about the protagonist's mother that first compel the boy to enter the tower, setting the entire adventure in motion. Despite its deceptive nature, it is forced to comply when ordered to guide the protagonist and an elderly maid into the fantasy realm. The relationship between the protagonist and the Gray Heron is the film's most dynamic. It begins with open antagonism, as the protagonist attacks the heron, breaking its beak and exposing its true, vulnerable form. This confrontation marks a turning point, after which their relationship slowly evolves into an unlikely alliance. The protagonist even helps the heron by plugging the hole in its beak, restoring its ability to fly. By the film's climax, the heron acts as a true companion, sneaking into the parakeet kingdom to free the protagonist from captivity. In the end, it bids the boy farewell as a friend, acknowledging the bond they have formed.

The Gray Heron undergoes a notable development, shifting from a menacing and deceptive harasser to a helpful, almost relatable ally. Its notable abilities are closely tied to its dual nature. As a bird, it can fly, but this ability is compromised when its beak is damaged. Its true talent lies in deception; it can create lifelike illusions, such as a watery imitation of the protagonist's mother, to manipulate others. Perhaps its most profound ability is its knowledge of the magical world's rules, including its power to make the protagonist forget his otherworldly adventures once they return to reality. While grotesque and untrustworthy at first, the Gray Heron proves to be an essential and ultimately faithful companion on the protagonist's path to healing.