A former yokozuna named Inochiriki, forced into retirement by a career-ending injury, has lost his sense of purpose. His life changes when a wealthy and influential patron, a tanimachi, summons him. The patron reveals a hidden world beneath the public face of sumo: a secret underground tournament where sixteen of the most formidable fighters in the world, each calling themselves a chikarabito, gather on a hidden dohyo. The rules are simple and brutal: true strength is not decided in the official arenas but here, in the shadows, where the tournament will determine who is genuinely the strongest of all. Inochiriki’s competitive fire is reignited as he answers the challenge, stepping onto a stage where no holds are barred and every match is a fight for survival and pride.

The story follows the bracket of the grand underground tournament, featuring a diverse roster of wrestlers with wildly different physiques, styles, and motivations. Among them are Ukon, a rival with a devastating right arm; Tokuronuma, a technician who can neutralize even the strongest attacks; the lightest competitor at only 98 kilograms, Shohei, who relies on speed against overwhelming size; and the heaviest at 285 kilograms, Oshimofuri, a mountain of a man. The current reigning yokozuna of the surface sumo world, Mongoryu, also descends into the underground arena, drawn by the promise of a true test. Other warriors include the ruthless Rōhyō, who breaks an opponent’s arm; the determined Kokushishin, who refuses to give up even with a broken limb; the striking specialist Usagi; the stubborn pusher-thrust specialist Shūmaru; and the Mongolian fighter Mōhakurō, seeking to settle a past humiliation against Mongoryu.

The narrative arcs unfold match by match, each bout revealing the fighters’ backstories and the depth of their resolve. Inochiriki’s journey is central, as he must push past his physical limitations and rediscover what it means to fight at full power. The tournament builds to a climax as the competitors’ paths converge, culminating in confrontations that test both body and spirit. The series is a focused, adrenaline-fueled sports battle story, driven by the intensity of each sumo clash and the personal stakes of every chikarabito who has staked everything on being the strongest underground.