Juli is a small, gray pet squirrel who has been a constant companion to the main character, Ema, since her early childhood. He has a distinct appearance, featuring a gray coat with darker gray stripes on his head, body, and tail, complemented by a fluffy white underside and cheeks. He is almost always seen wearing a pink ribbon with white polka dots tied into a bow around his neck. Despite being an animal, Juli possesses a complex personality and is capable of human speech, though his ability to communicate verbally is shared only with Ema and one of the Asahina brothers, Louis. This unique ability sets him apart as more than just an ordinary pet, serving as a guardian, confidant, and advisor to Ema.

Juli is fiercely loyal to Ema, with his primary motivation being to protect her from any perceived threat. His personality is defined by this protective nature, which often manifests as hostility, vigilance, and suspicion, particularly towards the thirteen Asahina brothers who become Ema’s new family members. He frequently refers to the brothers as wolves or monsters, believing they pose a danger to Ema and will try to take advantage of her. While his default stance is one of distrust, his attitude toward specific brothers varies. He shows particular trust and bonding with Louis, who is the only brother who can understand him, and the two even form a pact to protect Ema, referring to themselves as her knights. In contrast, he is openly hostile towards others, such as Kaname, whose flirtatious behavior earns Juli's immediate and physical disapproval, and Fuuto, whom he hates regardless of his actions. His responses to others are based on their behavior towards Ema; for instance, he becomes enraged when he learns Ema stayed at Natsume’s apartment or when Subaru confesses his feelings directly in front of him.

In the story, Juli acts as Ema’s primary protector and voice of caution, often hissing at her new brothers to keep them at bay. He is her steadfast companion as she navigates the complex dynamics of living in a household of thirteen men. A notable aspect of Juli's development is his appearance in a dream as a handsome, silver-haired man in a suit. In this human form, he confesses his love to Ema and reveals crucial information about her true origins as an adopted child, demonstrating that his connection to her goes beyond that of a simple pet and that he holds deep, significant knowledge about her past. Beyond his ability to speak, Juli has no other supernatural abilities but is highly intelligent and perceptive, able to sense when Ema is emotionally distressed even without visible signs like tears. He is also capable of physically intervening, having been known to strike the brothers in the face when he feels Ema is being wronged.