In the fourth installment of the fighting franchise, Boyka is shooting for the big leagues when an accidental death in the ring makes him question everything he stands for. When he finds out the wife of the man he accidentally killed is in trouble, Boyka offers to fight in a series of impossible battles to free her from a life of servitude.

Russian inmate Boyka, now severely hobbled by the knee injury suffered at the end of Undisputed 2. No longer the feared prison fighter he was, he has declined so far that he is now good only for cleaning toilets. But when a new prison fight tournament begins - an international affair, matching the best fighters from prisons around the globe, enticing them with the promise of freedom for the winner - Boyka must reclaim his dignity and fight for his position in the tournament.

Heavyweight Champ George "Iceman" Chambers is sent to a Russian jail on trumped-up drug charges. In order to win his freedom he must fight against the jailhouse fighting champ Uri Boyka in a battle to the death. This time he is not fighting for a title, he is fighting for his life!

Fai, once a world champion in boxing, escapes to Macau from the loan sharks and unexpectedly encounters Qi, a young chap who is determined to win a boxing match. Fai becomes Qi's mentor and rediscovers his passion to fight not only in the ring but for his life and the cares.

Monroe Hutchens is the heavyweight champion of Sweetwater, a maximum security prison. He was convicted to a life sentence due to a passionate crime. Iceman Chambers is the heavyweight champion, who lost his title due to a rape conviction to ten years in Sweetwater. When these two giants collide in the same prison, they fight against each other disputing who is the real champion.

这次新一季TV动画《刃牙》是时隔十几年的新作品，改编自板垣惠介创作的同名系列漫画中第二部的最凶死囚篇剧情。 世界各地共时性地越狱的五名最凶死刑犯，为了知道“败北是什么”，來到了世界最强战士聚集着的东京，与上一部出场战士们展开激战。本部战斗为竞技场外的无规则战斗，包含了任何武器与偷袭的使用。主角范马刃牙接受德川光成的邀请和五名死刑犯进行无规则的对決，并和松本梢江交往，最后因死刑犯柳龙光的毒手攻击而中毒。