Chaco Ishibashi, whose name is sometimes romanized as Chako, is a central character in the series. She is a normal middle school girl attending what seems to be an ordinary school and navigating the usual experiences of a student her age. Her role in the story is primarily defined by her perspective as an observer; she is the one character who notices a singular oddity in her otherwise unremarkable daily life. This oddity is her classmate, who sits at the desk next to her and is known as Shibainuko-san. Unlike everyone else around her, Chaco is acutely aware that Shibainuko-san does not look like a human but rather resembles a Shiba Inu dog.

Chaco's personality is not extensively detailed, but her actions reveal a curious and grounded nature. She is portrayed as an everyday student who is neither overly dramatic nor fantastical, which makes her observations about her peculiar classmate stand out. Her primary motivation stems from a simple but persistent confusion: she cannot understand why she seems to be the only person who perceives Shibainuko-san as a dog. Her classmates and teachers interact with the dog-like girl as if she were a completely normal human, showing no reaction to her unusual appearance. This disconnect between Chaco's perception and that of the people around her is the core driver of her experiences. She is not a hero or a detective, but simply a regular girl trying to make sense of a very strange situation that no one else acknowledges.

The key relationship in the story is between Chaco and her friend Naho, as the two of them often share in the small adventures and observations regarding their canine classmate. Chaco also has a brother named Yuuto, who appears as a supporting character. Her role in the story is that of a relatable audience surrogate. Through her eyes, the viewer is introduced to the show's central comedic premise: the bizarre contrast between a normal school setting and the presence of a character with the full appearance and mannerisms of a Shiba Inu, who is treated with complete normality by everyone except for Chaco. Little information is available concerning any significant character development over the course of the series or any notable abilities possessed by Chaco, as her defining trait is her mundane humanity.