"X" is a manga series created by Clamp, set in a world where the fate of humanity hangs in the balance between two opposing forces: the Dragons of Heaven and the Dragons of Earth. The story centers on Kamui Shiro, a young man who returns to Tokyo after a long absence following his mother's death. Kamui is revealed to be the key figure in an ancient prophecy, destined to decide the future of the world. His childhood friends, Fuma and Kotori Monou, are also deeply connected to this prophecy, with Fuma eventually becoming Kamui's greatest adversary.

The Dragons of Heaven, led by Princess Hinoto, aim to protect humanity and preserve the Earth, believing that humanity's survival is worth the sacrifices required. In contrast, the Dragons of Earth, led by Hinoto's twin sister Kanoe, seek to destroy humanity, viewing it as a corrupting force that must be eradicated to save the planet. Kamui is torn between these two factions, struggling to reconcile his personal desires with his role in the prophecy. His choices are further complicated by his deep bond with Fuma, who becomes the Kamui of the Dragons of Earth, and his protective feelings for Kotori, who becomes a tragic figure caught in the conflict.

The narrative unfolds through a series of intense battles, emotional confrontations, and revelations about the characters' intertwined destinies. Each member of the Dragons of Heaven and Earth possesses unique supernatural abilities, and their clashes are both physical and ideological. The story explores themes of fate, free will, and the consequences of choice, as Kamui grapples with the weight of his decisions and their impact on those he loves. The series is marked by its intricate plot, complex character relationships, and a sense of impending doom as the world teeters on the brink of destruction.