"The Mysterious Cities of Gold" is a 39-episode anime series set in the 16th century, blending historical fiction with elements of science fiction and adventure. The story begins in Barcelona, Spain, where a young orphan named Esteban lives under the care of a priest. Esteban possesses a unique ability to summon the sun, a power tied to his mysterious origins. His life changes when he encounters Mendoza, a navigator and adventurer, who reveals that Esteban’s father may have been connected to the legendary Cities of Gold, a fabled treasure sought by explorers of the era.

Esteban joins Mendoza on a journey across the Atlantic Ocean to the New World, accompanied by Zia, an Incan girl who was taken from her homeland by Spanish conquistadors, and Tao, the last descendant of the sunken empire of Mu. Together, the trio embarks on a quest to uncover the truth behind the Cities of Gold, which are said to hold immense wealth and advanced technology. Their journey takes them through perilous landscapes, ancient ruins, and encounters with indigenous cultures, all while evading the schemes of antagonists like the Spanish governor Francisco Pizarro and the enigmatic Marinche, who seek the treasure for their own gain.

The narrative intertwines historical events, such as the Spanish conquest of the Americas, with fantastical elements, including advanced ancient civilizations and mysterious artifacts. The characters frequently face moral dilemmas, cultural clashes, and the consequences of colonialism, adding depth to their personal growth and relationships. Esteban’s quest for identity, Zia’s longing to reunite with her people, and Tao’s connection to his lost heritage drive the emotional core of the story.

As the series progresses, the protagonists uncover clues about the Cities of Gold, leading them to confront the truth about their own destinies and the legacy of the ancient civilizations that once thrived in the Americas. The story culminates in a revelation about the true nature of the Cities of Gold, blending historical intrigue with a sense of wonder and discovery. The series balances adventure, mystery, and character-driven storytelling, making it a compelling exploration of history, mythology, and human ambition.