Duke is a character from the magical world who appears as a familiar. His physical form is that of a small frog, with a red body marked by black stripes. In human terms, his age is considered to be around thirty years old, and his height is described as being comparable to that of a cigarette pack. His speech is often punctuated with a verbal tic that sounds like "kero". Despite his small and unassuming appearance, Duke possesses a significant hidden history and a personality that contrasts between his typical lazy demeanor and moments of sharp insight.

As a familiar, Duke is summoned to serve and accompany Chocolat Meilleure, the main protagonist, on her journey in the human world. On the surface, his personality is sloppy, unreliable, and often discouraging. Rather than offering proactive help, he is frequently seen lounging around, sleeping, or making unhelpful comments about Chocolat's lack of progress compared to her rival. One of his stated hobbies is dancing, and he harbors a somewhat incongruous dream of becoming an idol singer. He also has a noted fondness for cake and other sweets.

Behind this lazy fa莽ade, however, lies a much more serious and capable individual. Duke is in reality Poivre Mayeur, a talented wizard and the younger brother of Cinnamon Mayeur, which makes him Chocolat鈥檚 maternal uncle. His transformation into a frog was a deliberate act of concealment. After hiding his sister Cinnamon when she was on the run, he became wanted by the palace guards and transformed himself to avoid capture, posing as a familiar. The spell, however, worked too well, and his magical power as a frog became too weak to allow him to change back on his own. This hidden identity explains his occasional lapses into more serious behavior and his possession of knowledge that an ordinary familiar should not have.

In both the manga and anime, Duke demonstrates a deeper involvement in the story than his role as a simple servant suggests. He shows familiarity with powerful characters he should not know, such as Pierre, whose real name he speaks while breaking through the boy鈥檚 magical barrier. He also appears to know secrets regarding Chocolat and her family history. When the situation demands it, he sheds his lazy persona and becomes a crucial source of information and protection, such as advising Chocolat on a magical drug or recognizing a royal magical item. His key relationships include a constant rivalry with Blanca, the white mouse who serves as Vanilla鈥檚 familiar, with whom he frequently argues. His most important relationship is with Chocolat, where he ultimately acts as a hidden guardian and family member. In the manga, his service as a familiar ends when Chocolat obtains a white frill heart, which frees him and allows him to return to his original human form as Poivre. Upon regaining his human form, he reveals further frightening secrets about Chocolat鈥檚 past. In the anime, his true identity is not fully explored, and he remains in his frog form, though he does briefly appear as a wizard once, retaining his sharp and critical attitude towards Chocolat.