"Baki Gaiden: Kenjin" is a spin-off manga series set within the expansive universe of the "Baki the Grappler" franchise. The narrative centers on Mitsunari Tokugawa, a prominent figure in the underground fighting world and a recurring character in the main series. Tokugawa serves as a manager and promoter for underground martial arts tournaments, often facilitating high-stakes battles between formidable fighters. The series delves into his backstory, exploring his rise to prominence and the challenges he faces in maintaining order and integrity within the brutal and chaotic world of underground combat.

The plot intertwines Tokugawa's personal journey with the broader dynamics of the underground fighting scene. It highlights his relationships with various fighters, including legendary martial artists and emerging talents, as well as his interactions with influential figures who seek to manipulate or exploit the tournaments for their own gain. Tokugawa's role as a mediator and strategist is central to the story, as he navigates political intrigue, rivalries, and the ever-present threat of violence.

Key characters include Tokugawa himself, portrayed as a shrewd and resourceful individual with a deep understanding of martial arts and human nature. The series also features appearances by iconic fighters from the "Baki" universe, such as Yujiro Hanma and Doppo Orochi, whose actions and decisions often influence the direction of the narrative. New characters are introduced, each with unique fighting styles and motivations, adding depth to the underground fighting ecosystem.

Thematically, "Baki Gaiden: Kenjin" explores the balance of power, loyalty, and ambition within a world where strength and skill are paramount. It examines the moral complexities of Tokugawa's role as a facilitator of violence, as well as the personal sacrifices he makes to uphold his vision of a fair and honorable fighting arena. The series maintains a focus on intense martial arts action, strategic maneuvering, and the intricate relationships that define the underground combat community.