Chiko is a small, fuzzy, unidentified creature with white fur who appears as a supporting character. This adorable and friendly being is found by the protagonist, Ren, at the beginning of the story in the human world, specifically in the back alleys of Shibuya. From the moment they meet, Chiko becomes a constant and devoted companion, remaining by the boy's side throughout his many trials and tribulations. Chiko is hardly ever seen far away from Ren, who is later renamed Kyuta, and is most frequently seen perched contentedly on top of the boy's head.

Chiko's role in the narrative is primarily that of a supportive presence and a source of comfort. The character provides a calming and light-hearted counterbalance to the film's more serious themes of trauma, loneliness, and the struggles of growing up. Beyond this function, a widely discussed interpretation suggests a deeper, more profound purpose. The ending of the film implies, though does not explicitly confirm, that Chiko may be the reincarnation of Ren's deceased mother. This theory is supported by several key moments of inexplicable, intelligent intervention. For instance, Chico appears to Ren in his darkest hour of despair, and at a pivotal moment when Kyuta is on the verge of being consumed by murderous rage and darkness, Chiko bites him, snapping him back to his senses. This act is interpreted not as a random animal reflex, but as the protective gesture of a mother refusing to let her son lose his soul. Furthermore, when Kyuta is training to master a difficult technique known as the sword in the heart, he sees a vivid vision of his mother precisely when Chiko is resting against him, suggesting the creature's proximity awakened a deep, subconscious memory that enabled an emotional breakthrough.

Chiko's most significant relationship is unquestionably with Ren or Kyuta. The small beast's dedication is unwavering, and it stays with the boy as he transitions from a lost, runaway child to a powerful young man living in the beast realm of Jutengai. Through all the conflicts, including the climactic battle against a darkness that threatens both the human and beast worlds, Chiko remains a steadfast, if small, ally. The character's development is not one of personal change but of a growing revelation of its potential true nature. Starting as a simple, cute creature picked up off the street, Chiko’s actions throughout the story hint at a guiding intelligence and a deep, protective love that transcends its small form, ultimately suggesting a spiritual connection to the protagonist’s past. As a being, Chiko possesses no notable combat abilities or supernatural powers beyond its unwavering loyalty and its comforting presence. The creature's most significant ability may be its mysterious, intuitive sense for guiding Kyuta away from a path of darkness and toward emotional healing.