Koitaro Samejima is the son of Karyu, a former ozeki who was notorious for his foul mouth and vicious style inside the ring. Young Koitaro worshipped his father's raw power and unapologetic attitude, but everything changed when Karyu was involved in a bar fight that injured several people. The incident led to his expulsion from the sumo league, and the proud, formidable wrestler Koitaro had admired was gone. In the years that followed, Karyu's life spiraled downward, and he eventually died after recklessly challenging a truck in a tackling match. Despite this tragic downfall—or perhaps because of it—Koitaro cannot resist the pull of the sumo world. Driven by his father's legacy and the question of what it truly means to give everything, he enters professional sumo determined to challenge every opponent in his path and rise to the top.

The story is set in the highly structured and hierarchical world of professional sumo, depicted with a strong emphasis on realism. It follows Koitaro from his very first steps in the sport, starting in the lowest jonokuchi division and climbing through the ranks by fighting in tournament after tournament. The manga portrays not only the matches themselves but also the grueling training, the strict communal life inside the sumo stable, the complex relationships between wrestlers, and the psychological and physical toll the sport takes on its athletes.

Koitaro is a relatively small and slender wrestler at 176 centimeters, but he compensates with extraordinary physical abilities honed through unique training and an unbreakable fighting spirit. His signature style is built around powerful thrusting techniques known as buchikamashi and brutal hand-slaps, and he later adds grappling techniques and throws to his arsenal. Throughout his journey, he faces a wide array of rivals who push him to grow both technically and mentally. Chief among them is Oko Kenichi, the son of former yokozuna Torashiki and Koitaro's greatest rival, whose own talent and cold, calculating approach to sumo create a fierce, generational clash between their families. Other key figures include his stablemates, such as the massive Hakusui (who adopts the shikona Agyou) and the more technical Ungyou, as well as later additions to the stable like the collegiate champion Tsunematsu and the reclusive youth Maruyama Daikichi.

The narrative is structured across three interconnected arcs. The first part, simply titled Bachi-Bachi, covers Koitaro's childhood, his entry into the sumo stable run by former komusubi Haruryu, his early struggles as a delinquent learning discipline, and his rise from the lowest divisions through the ranks of jonokuchi and jonidan. The second part, Bachi-Bachi Burst, follows his ascent through the highly competitive makushita division, where he faces increasingly skilled opponents and his rivalry with Oko intensifies, culminating in a hard-fought tournament victory. The final arc, Samejima, Saigo no Juugonichi (Samejima's Last Fifteen Days), leaps forward five years. Koitaro is now a popular maegashira-ranked wrestler in the top makuuchi division, adored by fans but fighting with a body that is breaking down from years of relentless, head-on combat. The arc chronicles a single harrowing fifteen-day tournament as he battles through chronic injuries and the looming threat of chronic traumatic encephalopathy, facing off against former rivals who have also risen to the top, including Oko who has become an ozeki, and finally setting up a climactic challenge against the undefeated yokozuna Hoyou. The series ends abruptly and prematurely at the end of day thirteen of this final tournament due to the sudden passing of the author, leaving Koitaro's ultimate fate and the outcome of his final match unwritten.