"Tough" is a martial arts manga series that centers on the journey of Kiichi Miyazawa, a young man deeply rooted in the world of underground fighting. The narrative begins with Kiichi, who has been trained in the secret martial art of Nadashinkageryu by his adoptive father, Seiko Miyazawa. This fighting style, passed down through generations, emphasizes brutal and unorthodox techniques designed for real combat. Kiichi's life takes a dramatic turn when he discovers that his biological father, the legendary fighter Kiryu Miyazawa, is alive and has been imprisoned. Determined to uncover the truth about his family and prove his strength, Kiichi enters the dangerous world of underground fighting tournaments.

The story unfolds as Kiichi faces a series of formidable opponents, each with their own unique fighting styles and motivations. These battles are not merely physical confrontations but also tests of Kiichi's resolve, skill, and understanding of his martial arts heritage. Along the way, he encounters allies and rivals, including his half-brother Ryu Miyazawa, who shares a complicated relationship with Kiichi due to their shared lineage and differing philosophies on combat. The rivalry between the brothers becomes a central theme, driving much of the narrative tension.

As Kiichi progresses through the underground fighting circuit, he uncovers deeper layers of intrigue involving the Nadashinkageryu school, its history, and its connection to his family. The series delves into themes of legacy, honor, and the moral complexities of violence. Kiichi's journey is marked by personal growth, as he grapples with the weight of his father's legacy and his own identity as a fighter. The narrative is punctuated by intense, high-stakes battles that showcase a variety of martial arts techniques, blending realism with dramatic flair.

The supporting cast includes a range of characters who influence Kiichi's path, from fellow fighters to mentors and adversaries. Each character brings their own backstory and motivations, adding depth to the overarching plot. The series also explores the darker aspects of the fighting world, including corruption, betrayal, and the psychological toll of constant combat. Through its intricate storytelling and dynamic fight sequences, "Tough" presents a compelling exploration of martial arts, family, and the relentless pursuit of strength.