"Sweet Little Devil" centers on a young girl named Miu, who lives a seemingly ordinary life until she discovers she is the daughter of a demon king. This revelation comes with the knowledge that she must fulfill her destiny by taking over her father’s throne in the demon world. However, Miu is reluctant to embrace her demonic heritage, as she values her human life and friendships. Her internal conflict is further complicated by the arrival of a demon butler named Claude, who is tasked with guiding her and ensuring she accepts her role as the heir to the demon throne.

The narrative explores Miu’s struggle to balance her human identity with her demonic responsibilities. As she navigates this dual existence, she encounters various supernatural beings, including rival demons and otherworldly creatures, who either challenge or support her journey. Claude, while initially appearing as a strict enforcer of her demonic duties, gradually reveals a more complex personality, often acting as both a mentor and a protector. His presence adds tension and depth to the story, as his loyalty to the demon king sometimes clashes with his growing attachment to Miu.

Throughout the series, Miu’s relationships with her human friends play a significant role. These friendships are tested as her demonic powers begin to manifest, often leading to unintended consequences. The story delves into themes of identity, loyalty, and the struggle between fate and free will. Miu’s journey is marked by moments of humor, emotional conflict, and action, as she confronts both external threats and her own insecurities. The manga balances lighthearted moments with darker undertones, reflecting the duality of Miu’s existence and the challenges she faces in reconciling her two worlds.