Kousuke Ueki, a middle school student, is chosen by a celestial being named Mr. K to participate in a tournament where 100 candidates, each representing a different god, compete to determine the next ruler of the Celestial World. Each candidate is granted a unique power by their respective god, and they must recruit other humans to fight on their behalf. The ultimate goal is to collect "blank talents," which are earned by defeating opponents. The candidate who amasses the most blank talents will ascend as the new ruler, and their representative human will gain the ability to grant any wish.

Ueki is granted the power to transform trash into trees, a seemingly mundane ability that he creatively leverages in combat. He is joined by a group of allies, including Ai Mori, a classmate who wields the power to turn towels into iron, and Rinko Jerrard, who can transform her hair into weapons. Together, they face off against other candidates and their representatives, each possessing unique and often bizarre abilities. The battles are intense and strategic, with Ueki and his friends frequently overcoming seemingly insurmountable odds through teamwork, ingenuity, and sheer determination.

As the tournament progresses, Ueki uncovers darker truths about the competition. He learns that the gods are not benevolent overseers but manipulative entities who view humans as mere tools. The stakes escalate when it is revealed that the losing candidates and their representatives will be erased from existence, adding a layer of urgency and moral complexity to the conflict. Ueki’s resolve is tested as he grapples with the ethical implications of the tournament and the sacrifices required to protect his friends and ideals.

The narrative delves into themes of justice, loyalty, and the value of human life, with Ueki embodying a steadfast commitment to doing what is right, even in the face of overwhelming adversity. His journey is marked by personal growth, as he evolves from a carefree student into a determined leader who inspires those around him. The series balances action-packed battles with moments of introspection and character development, creating a compelling and multifaceted story.

Key antagonists include Robert Haydn, a ruthless candidate who seeks to exploit the tournament for his own gain, and Marilyn Cary, a manipulative and cunning opponent who challenges Ueki both physically and morally. The diverse cast of characters, each with distinct motivations and abilities, enriches the narrative and drives the plot forward. The Law of Ueki combines humor, drama, and high-stakes action to deliver a memorable and engaging manga experience.