In 1946 Kure, Shozo Hirono, a war veteran, is sent to prison after fatally stabbing a sword-wielding yakuza who attacked a friend, receiving a 12-year sentence. A brutal prison brawl leads to a moment of fragile alliance when he is placed in solitary confinement with Hiroshi Wakasugi of the Doi Family; the two men forge a sworn brotherhood through a blood oath. Wakasugi, determined to secure Hirono’s release, attempts a harakiri, vowing that if he survives, he will arrange Hirono’s freedom by pressuring the prison warden through the powerful Yamamori Family led by Yoshio Yamamori. Hirono is released, and his band of former soldiers—Tetsuya Sakai, Seiichi Kanbara, Shinkai Uichi, Masakichi Makihara, and Shuji Yano—swear loyalty to the Yamamori clan, sharing sake during a ceremonial pledge that is witnessed in part by the aging power broker Okubo Kenichi.
Three years slip by, and Hirono finds trouble again when he clashes with a man named Ueda at a gambling den. Ueda, a blood relative of Okubo, prompts Hirono to perform yubitsume as an apology. Okubo accepts the gesture but asks Yamamori to absorb Ueda into his family and to help influence a crucial vote for corrupt politician Shigeto Nakahara who backs a rival named Kanamaru, a political struggle pitting Yamamori’s faction against Doi’s. Tetsuya Sakai kidnaps and threatens one of Kanbara’s allies to tilt the balance, then disappears into hiding. Doi’s enforcers beat Kanbara and pressure Yamamori, triggering a temporary peace: Wakasugi becomes a guest member of Yamamori’s family, while Kanbara takes his place within the Doi Family.
Six months later, Doi shifts its strategy and partners with the Kaito Family from Hiroshima, moving against Yamamori. Wakasugi hints at killing his boss to end the entanglement, but Hirono reminds him that betrayal is forbidden by yakuza code. With no consensus among the sworn brothers, Hirono volunteers to handle the matter alone, and Yamamori agrees to leave him a stake in the family’s fortune. Hirono executes the hit on Doi during a meeting with the Kaito group and then goes into hiding. A later ruse brings Kanbara to lure Hirono out, but the plan backfires when another car opens fire. Hirono realizes he’s been abandoned by Yamamori and hunted by the Doi Family, and surrenders to the authorities. Wakasugi visits Hirono in prison, warns of Yamamori’s scheming, and eventually murders Kanbara before fleeing, only to be betrayed by an anonymous police tip that leads to his girlfriend’s family and a fatal gunfight with the police.
As the Korean War rages through the 1950s, the Yamamori Family prospers on war contracts but fractures as members turn to philopon, driven by heavy kickbacks. [Tetsuya Sakai], now a high-ranking officer, and [Shinkai Uichi] clash with Yamamori’s drug dealings. Arita, Shinkai’s lieutenant, ghost-writes a plan to reform the family’s structure so each member can be self-sustaining and reduce kickbacks; Toshio Arita oversees a brutal purge, killing Ueda, and the internal conflict erupts into violence: Sakai’s faction emerges victorious in the street battles, [Arita] orders a life sentence for a police officer, and Shinkai dies before he can flee the city by train.
Hirono is paroled once more, and Yamamori immediately asks him to kill Sakai, only to take him to a meal and leave him to pay the bill. Hirono learns that Yamamori has become a wealthy and calculating power broker. He visits the home of Wakasugi’s former partner to pay his respects and finds Sakai there with a new partner and a baby, narrating that Yamamori’s lies have riven their sworn circle and that Sakai plans to launch his own organization while negotiating with the Kaito Family. Makihara, a survivor who remains loyal to Hirono’s former allies, informs Hirono that Yano is pressing the Kaito Family to end negotiations. Hirono refuses Sakai’s offer to join and instead announces his own detachment from Yamamori, while Makihara and Hirono’s faction reveal the truth about the past betrayals. As the two men vow to settle their score, Makihara’s assassins strike Sakai, killing him at a toy shop for his child. At Sakai’s funeral, Makihara and Yamamori are in attendance, and Hirono arrives with a gun, shatters the display, and hurls a final threat at Yamamori before walking away, leaving the violent world of loyalties and debt to endure its endless cycle.
