"Agū: Tensai Ningyō" is a historical fantasy manga series set in the late Edo period of Japan. The narrative centers on Agū, a young girl who is not entirely human but rather a "ningyō," a humanoid creature created through alchemy. Agū possesses extraordinary intelligence and physical abilities, making her a target for those who seek to exploit her unique nature. The story begins with Agū being discovered by a wandering puppeteer named Ushimatsu, who takes her under his wing and becomes her protector. Together, they embark on a journey across Japan, encountering various individuals and factions with conflicting intentions toward Agū.

The plot delves into the moral and ethical dilemmas surrounding Agū's existence. As a being created through forbidden alchemy, she is both revered and feared. Some view her as a miracle, while others see her as an abomination. This duality drives much of the conflict in the series, as Agū struggles to understand her place in the world and the true nature of her creation. Ushimatsu, while initially motivated by self-interest, gradually develops a paternal bond with Agū, striving to shield her from those who would harm or manipulate her.

Key characters include Agū, whose innocence and curiosity contrast with her immense power; Ushimatsu, whose pragmatic and often cynical outlook is challenged by his growing attachment to Agū; and a range of antagonists, including alchemists, government officials, and religious figures, each with their own agendas regarding Agū's fate. The series explores themes of identity, humanity, and the consequences of scientific ambition, set against the backdrop of a society on the cusp of modernization.

The narrative is structured around episodic encounters, with each arc introducing new characters and challenges that further develop Agū's understanding of herself and the world. The series balances action, emotional depth, and philosophical inquiry, creating a layered story that examines the complexities of human nature and the ethical boundaries of creation. Through its exploration of Agū's journey, "Agū: Tensai Ningyō" offers a thought-provoking reflection on the intersection of science, morality, and the human condition.