"MeiKing" is set in a world where ancient spirits known as "Mei" coexist with humans, bound by a delicate balance maintained through sacred rituals and contracts. The story centers on Kaito, a young man who inadvertently becomes the vessel for the most powerful Mei, the "MeiKing," after a ritual goes awry. This event disrupts the equilibrium between the human and spirit realms, triggering a series of conflicts as rival factions seek to control or destroy the MeiKing's power.

Kaito, initially unaware of the significance of his newfound abilities, is thrust into a world of political intrigue and supernatural warfare. He is guided by Yuna, a skilled Mei summoner, and Ren, a rogue spirit hunter, who help him navigate the complexities of his role. Together, they uncover the truth behind the MeiKing's origins and its connection to an ancient prophecy foretelling the collapse of the two realms if the balance is not restored.

The narrative explores themes of power, responsibility, and coexistence, as Kaito struggles to reconcile his humanity with the immense power he wields. Antagonists include the Shadow Council, a clandestine organization seeking to exploit the MeiKing for their own ambitions, and the Spirit Sovereigns, ancient Mei who view Kaito as a threat to their dominion. The series balances action-packed battles with moments of introspection, delving into the moral dilemmas faced by its characters.

Key supporting characters include Aiko, a historian with knowledge of the prophecy, and Haruto, a former ally of Kaito who becomes disillusioned with his choices. The story progresses through a series of arcs, each revealing more about the world's lore and the characters' motivations, culminating in a climactic confrontation that determines the fate of both realms. "MeiKing" combines elements of fantasy, adventure, and drama, offering a layered narrative that appeals to fans of intricate world-building and character-driven storytelling.