"Kengan Ashura" is a martial arts manga series set in a world where powerful corporations and wealthy individuals settle disputes through gladiatorial combat. These battles are fought by skilled fighters known as "Kengan matches," where representatives, or "gladiators," compete in brutal, no-holds-barred fights. The series primarily centers on Tokita Ohma, a mysterious and highly skilled fighter who becomes the representative for the Nogi Group, a powerful corporation led by Nogi Hideki.

Ohma, known as "The Ashura," possesses immense physical strength and a unique fighting style rooted in the Niko Style, a martial art passed down by his mentor. His journey begins when he is recruited by Yamashita Kazuo, a middle-aged salaryman who becomes Ohma's manager. Despite his initial lack of confidence, Yamashita grows into his role, providing both logistical support and emotional grounding for Ohma as they navigate the dangerous world of Kengan matches.

The narrative unfolds during the Kengan Annihilation Tournament, a massive event organized by the Kengan Association to determine the strongest fighter and, by extension, the most influential corporation. The tournament brings together a diverse array of fighters, each with their own unique techniques, backgrounds, and motivations. Notable participants include Wakatsuki Takeshi, a superhumanly strong fighter with decades of experience; Gaolang Wongsawat, a master of Muay Thai and boxing; and Kuroki Gensai, a stoic and deadly karate practitioner. Each fighter represents a different corporation, and their battles are as much about personal ambition as they are about corporate dominance.

As the tournament progresses, Ohma faces increasingly formidable opponents, revealing more about his past and the origins of his fighting style. Flashbacks explore his harsh upbringing, his training under the enigmatic Niko, and the tragic events that shaped his ruthless determination. The series delves into themes of survival, loyalty, and the pursuit of strength, with Ohma's journey serving as the emotional core of the story.

The supporting cast plays a significant role in fleshing out the world of "Kengan Ashura." Characters like Kaede Akiyama, a journalist investigating the Kengan Association, and Rino, a cunning and manipulative businesswoman, provide insight into the political and economic machinations behind the matches. The fighters themselves are given depth through backstories and personal stakes, making their battles more than just physical confrontations.

The series is characterized by its intense, detailed fight scenes, which showcase a wide variety of martial arts styles and techniques. The fights are often brutal and visceral, emphasizing the physical and psychological toll on the combatants. The manga balances these action sequences with moments of character development and world-building, creating a narrative that is both engaging and immersive.

By the conclusion of the Kengan Annihilation Tournament, the story explores the consequences of the battles and the shifting power dynamics within the Kengan Association. Ohma's journey, marked by both triumph and tragedy, leaves a lasting impact on the world of corporate gladiators, setting the stage for further developments in the series' sequel, "Kengan Omega."