"The Moon and The Sun" is a historical fantasy manga set in 17th-century France, blending elements of court intrigue, supernatural phenomena, and personal drama. The narrative centers around Marie-Josèphe, a young woman of noble birth who becomes entangled in the opulent yet treacherous world of the French royal court at Versailles. Her life takes a dramatic turn when she is tasked with caring for a mysterious sea creature captured by her brother, Yves, a naval officer and scientist. This creature, referred to as the Sea Monster, is believed to hold the key to immortality, a secret that King Louis XIV desperately seeks to unlock.

Marie-Josèphe forms an unexpected bond with the Sea Monster, discovering that it possesses intelligence, emotions, and a connection to ancient myths. As she delves deeper into the creature's origins, she uncovers a web of political machinations, scientific ambition, and moral dilemmas. Her brother, Yves, is torn between his loyalty to the king and his growing unease with the unethical treatment of the creature. Meanwhile, Marie-Josèphe's interactions with the Sea Monster challenge her understanding of humanity, divinity, and the natural world.

The story explores themes of power, morality, and the clash between science and superstition. The court of Versailles serves as a backdrop of extravagance and decadence, where characters navigate alliances, betrayals, and personal ambitions. Marie-Josèphe's journey is one of self-discovery and defiance, as she confronts societal expectations and fights to protect the Sea Monster from exploitation. The narrative weaves together historical accuracy with fantastical elements, creating a rich tapestry of intrigue and emotion. The characters are complex, with their motivations and conflicts driving the plot forward, making "The Moon and The Sun" a compelling exploration of human nature and the consequences of unchecked ambition.