Carlo Rossetti is the father of the protagonist, Dahlia Rossetti, and a central figure in her life even after his death. A highly skilled and respected magical toolmaker, Carlo earned the title of Baron of Honour for his numerous successful inventions and contributions to the field. He is also the founder of the Rossetti Trading Company, which Dahlia later inherits and revitalizes. As a single father, he raised Dahlia with great love and care after his wife left the family following Dahlia's birth. His known abilities lie in his exceptional craftsmanship and his keen understanding of the commercial and social aspects of the magical tool trade. He was capable of creating various magical objects that enriched people's lives, a talent that garnered praise and respect from colleagues and business partners like Ivano Badoer.

In his daily life, Carlo could be careless and disorganized, a trait that contrasted with his professional competence. However, his affection for his daughter was evident in his actions and long-term planning. Aware of his declining health, he was motivated by a deep concern for Dahlia's future security and happiness. This led him to arrange an engagement between Dahlia and his official apprentice, Tobias Orlando, believing it would provide her with a stable partnership and protect her legacy within the craft. This decision stemmed from his desire that she would not end up alone or destitute after his passing. In a further strategic move to safeguard her, Carlo cultivated numerous debts of favour with various individuals and organizations connected to his work. He left these connections as a final testament, explicitly requesting that she not be informed of these arrangements until she naturally came into contact with each person. This ensured that Dahlia would encounter a network of allies predisposed to assist her without her feeling indebted or guided by his influence from beyond the grave.

His role in the story is primarily as a foundational influence and a posthumous protector. Dahlia's passion for creating magical tools is a direct result of growing up surrounded by his work and receiving his mentorship. Their relationship was one of mutual admiration and collaboration, with Carlo often recounting his daily experiences to her and supporting her early experiments, such as her development of a water-repellent fabric. Dahlia is known to be a "Daddy's Girl," completely devoted to her father, and his sudden collapse and death at the Merchants' Guild is a devastating turning point in her life, leaving her heartbroken but determined to continue his legacy. His death also forces the postponement of her planned wedding to Tobias, setting the stage for the subsequent annulment and Dahlia's journey toward independence. Extra stories at the end of each light novel volume provide further glimpses into his past and reveal hidden episodes from his life that Dahlia never knew.