In a post-apocalyptic world, there was a deadly martial art form known as Hokuto Shinken. There were four brothers that were trained by their master, and essentially their adoptive father, in the art. Due to his affinity for love over power, the youngest brother, Kenshiro, was chosen to be the successor.
This angered two of the three other brothers. The oldest, Raoh, left home, vowing to take over the entire land left after the apocalypse, to prove himself the most worthy successor. The second oldest, Jagi, challenged Kenshiro. After his defeat, Jagi was left with a disfigured head and used a helmet to hide it. The third oldest brother, Toki, chose to use Hokuto Shinken as a healing art.
When Kenshiro left home to train to become worthy of the title of successor Hokuto Shinken, he met a woman named Yuria. They became engaged to be married, however, a man named Shin desired Yuria. Shin beat Kenshiro nearly to death, leaving seven wounds in his chest resembling the Big Dipper constellation. Kenshiro was spared when Yuria declared her love for Shin, even though she still loved Kenshiro.
Raoh defeated every person he fought and became ruler of a group of bandits. Now calling himself Lord Ken-oh, one of his servants, Nadai, made him aware of a long-forgotten relic from the atomic war, a sphere city housing a nuclear arsenal. Since he sought power but did not wish to destroy the rest of the world, he told Nadai to use the resources from the sphere city to build a thriving city surrounding it. Lord Ken-oh told him to become ruler of the city, but to keep the actual purpose of the sphere city a secret in order to keep it from being activated. Nadai built this city of miracles, Eden, up in a single generation.
Eden thrived and no one entered the sphere city until Nadai's wife was shot. Knowing that the sphere city contained a bed that would heal wounds, he brought his wife into the chamber. The bed triggered an hourglass that would set off its nuclear arsenal once the last piece of sand fell, so Nadai's wife told her husband that the cost was too great. Understanding his wife's wishes and wanting to spare her from a slow, painful death, Nadai killed her swiftly by his own hand. However, he didn't know that his daughter, Xsana, was watching. Xsana thrust her dagger into Nadai and told the people of Eden that Lord Nadai had died, but spared the specific details.
Yuria felt that she was forced into a loveless relationship and tried to commit suicide but was saved by Lord Ken-oh. With her body slowly dying, Lord Ken-oh sent a letter stating that she must be let into Eden and into the sphere city within. There, Yuria climbed up to the top of sphere city and laid down on the bed inside. After she laid on the bed, the doors to sphere city closed, and her wounds began to heal.
Days afterward, Kenshiro learned that Yuria was alive and that she was in Eden. He then managed to get into Eden by allowing himself to be captured by Jagre, the captain of Eden's watch, the city's militia. Jagre had a hatred for martial artists, so he placed Kenshiro in prison. Kenshiro entered the challenge in the Coliseum, where prisoners fight each other to the death. The winner was said to be able to ask Lady Xsana for one request, and Kenshiro simply requested to be let into Eden so that he could look for Yuria.
Lady Xsana granted Kenshiro's request and had Jagre give him a tour of the city. Jagre did so, reluctantly, and gave Kenshiro 5,000 IDL, which were coins minted by Eden to act as currency. He gave Kenshiro a warning that he'd have to earn more legitimately, as Jagre would be watching him. Kenshiro earned enough to get by doing favors as well as working as a bartender, a bounty hunter, and a merchant for a stall managed by his sidekick, Lin.
Kyo-oh, the leader of the Army of Ruin, and his second in command, Targa, rammed their trucks into Eden, destroying their gate. Kenshiro beat Targa, but Kyo-oh took him before Kenshiro could kill him. Jagre, the leader of Eden's watch, the city's militia, tried to shoot Kyo-oh. However, Kyo-oh used a deadly martial art, Meito Kieiken, which caused him to start spasming. Kenshiro and Lady Xsana took him to Rihaku, Eden's only doctor, and learned that Kyo-oh's martial art was electrical in nature and affected Jagre's mind just as Kenshiro's affected people's bodies.
Kenshiro and Rihaku had Kenshiro's young sidekick and amateur mechanic, Bat, use junk parts to fix a truck. They then ventured out in the wasteland to Cassandra, the prison where Lord Ken-oh imprisoned Jagi, his pacifist brother. Jagi healed Jagre's mind and vowed to teach Kenshiro everything he has learned about Hokuto Shinken so that he could put an end to their older brother's cruel intentions.
Once they returned to Eden, Xsana told Kenshiro that a man named Rei
claimed that a man with seven scars on his chest had kidnapped his sister Airi. It was revealed that Rihaku was the person who told Rei to go to Eden. He did so, despite knowing Kenshiro was innocent, in order to prove that Kenshiro was worthy to protect Yuria. Kenshiro had lost to a Nanto Seiken fighter, Shin, before, and Rihaku wanted to be sure his martial arts expertise had truly improved.
Xsana had Kenshiro battle Rei to prove his innocence. Kenshiro did so but spared Rei's life as he knew Rei only was fighting him as he thought Kenshiro took his sister. After the fight, it was revealed that Airi was in Eden. However, due to her sexual abuse from forced servitude, she chemically blinded herself. Kenshiro used Hokuto Shinken to heal her, showing that the martial art could heal as well as kill.
After Kenshiro was proven innocent, Xsana told him what had happened to Yuria, but she didn't know if Yuria had managed to make it up to the bed at the top of the sphere city. Xsana told Kenshiro that the only way to know for sure would be to climb the mountain overlooking the city. However, the only way to get there would be to cross through the Cursed Village.
The Cursed Village got its name due to the fact that people of Eden who had been mysteriously changed into mindless zombies were brought there to protect the people of Eden from them. However, upon seeing the cursed villagers, Kenshiro realized they exhibited some of the same traits that Jagre had but much more severe. Kenshiro was able to use Hokuto Shinken on them, however they were too far gone. They turned back to their previous state for mere minutes before dying.
Kenshiro traveled up to the mountain peak while Jagre stayed behind to prepare the villagers for a proper burial. At the peak, Kenshiro discovered that Nadai was still alive. He explained that he hid the fact that he was still alive, as he didn't want to put Xsana in a conflict that would prevent her from focusing on ruling and protecting Eden.
Kenshiro also saw that Yuria was alive and healing in the bed in the chamber atop Sphere City. He didn't have too long to reflect on that, as the empire led by Emporer Thouzer attacked Eden while it was still vulnerable since the entrance hadn't yet been fully repaired.
Jagre, Kenshiro, and the rest of Eden's watch defeated the men of the empire, while Kenshiro went to Eden's nightclub to rescue Xsana, who had been kidnapped by Thouzer. Kenshiro fought Thouzer, who claimed that he was immune to Hokuto Shinken. However, during their fight, Kenshiro realized Thouzer's secret that his organs were on the opposite side.
Kenshiro adjusted his martial arts and defeated Thouzer. Jagre and Rihaku told Thouzer that they had defeated his men. Xsana and Rihaku, at the protest of Jagre, allowed Thouzer to retreat. Thouzer went against his nature to admit defeat, as he claimed he would enjoy watching Kenshiro slowly break as he kept fighting people to keep the woman he loved, Yuria, safe.
Jagi, who had given himself identical scars to Kenshiro, so that he could commit crimes that would be blamed on his younger brother, kidnapped ten men around Eden that had a similar build to his own. He did this to try to trick Kenshiro, but after Kenshiro identified the real Jagi, it was revealed that Targa had teamed up with Jagi and had kidnapped Rei and Airi. While Kenshiro defeated Jagi, Nadai freed Rei and Airi. Kenshiro recognized that Nadai used Meito Kieiken, and realized that Nadai was Kyo-oh, the leader of the Army of Ruin.
Ken-oh arrived in Eden and told Xsana he had come for Yuria. When Xsana told him no one could enter Sphere City with the doors closed, Ken-oh stated that Nadai could open them. When Xsana told him that Nadai was dead, Ken-oh brought Yuria to the mountain peak to see for himself.
Ken-oh revealed that he sought Yuria as she was the successor of Nanto Shinken and the master of the last and most powerful of Nanto's skills. He was planning on taking Yuria out of Sphere City once she healed, but without Nadai that was impossible, so he began to aim a sphere at Yuria to kill her.
Kenshiro stopped him and revealed that Nadai was still alive. Kenshiro then beat his older brother in a fight, and Ken-oh said that he would let Kenshiro try to rescue her, and that he would return to finish their fight later.
Kenshiro revealed to Xsana and Jagre the truth about Nadai, and asked if they knew the whereabouts of the Army of Ruin's base. They didn't know, but they pointed him in the right direction. Eventually, Kenshiro heard of a sage of the desert and was led toward a motorcade east of Eden.
This turned out to be a trap, as Targa posed as Kyo-oh as Nadai entered Eden to open the sphere city and kill Yuria. Kenshiro defeated Nadai, but he was prevented from entering sphere city by Lyra, the manager of the nightclub, Jagre, and Targa. They sought revenge on Nadai, who had killed their fathers using Meito Kieiken in order to protect the secret of sphere city.
Targa turned on his compatriots, shooting Jagre, Lyra, and Nadai. He revealed that he lost half of his body during the war and was reconstructed with mechanical parts.
Targa felt that Nadai was the only person who could defeat him, due to his electrical implants and the fact that he had survived Hokuto Shinken two times previously. Kenshiro proved this assumption wrong, as he successfully hit Targa's pressure points, causing him to explode. Kenshiro closed the doors on the spheres, awakened Yuria from the chamber's bed, and prepared to die to save the world. However, Nadai pushed them into the bed and closed it, sacrificing himself to save their lives.
Afterward, Yuria and Kenshiro traveled in their buggy to an unknown destination after Kenshiro made a quick stop to deliver apples, the symbol of Eden.
