In 1535, Obayashi Kansuke, a masterless samurai, is on his way home to succeed his adoptive father after 15 years of journey studying military strategies. At a deserted village he drops in at, he saves a girl from a samurai. The samurai is one of the soldiers under Takeda Nobutora, the warlord of Kai, who are in the battle with the Imagawa clan of Suruga. The girl named Mitsu falls in love with Kansuke. Meanwhile, the Hojo family of Sagami invades the domain of Kai. Kansuke goes to watch the battle between the Takeda and Hojo armies. Though Kansuke has stopped her, Mitsu follows him and is caught by the soldier of the Takeda clan again.
Kansuke returns home in Mikawa Domain after 15 years. He brings the decapitated head of the samurai of the Takeda army he killed to save Mitsu—he have planned to show it as a display of his prowess in order to be taken into the service of the Imagawa clan. Coming back, Kansuke finds that his adoptive father now has a natural son. The father who wants the son, not Kansuke, to succeed him steals the head and tenders it to one of the warlords under the Imagawa clan as the son’s achievement. Kansuke decides to rename himself Yamamoto Kansuke, the family name of his real parents, and leaves Mikawa for Suruga, where his was born. In Suruga, Kansuke happens to know his elder brother Sadahisa is involved in a conspiracy against the head of the Imagawa family. For knowing the secret, Kansuke is attacked by a group of assassins directed by Sadahisa. Kansuke has to leave home again.
Kansuke goes back to the Kai domain, where he meets Mitsu. She is expecting a baby, whose father, she insists, is Kansuke. Though he refuses her once, Kansuke gradually becomes attached to the unaffected nature of the villagers and eventually makes up his mind to live there with Mitsu and the baby she is carrying. Meanwhile, the ruler Nobutora and his young son and heir Harunobu are on bad term. Nobutora wages wars one after another, provoking complaints against him among his retainers as well as common people. One day, Nobutora goes hunting to get nothing. Irritated, he shoots an arrow at a human—the woman aimed at is Mitsu.
Mitsu has been shot and killed by Nobutora. Kansuke keeps calm, but hearing Takeda’s retainers impose silence on the villagers about what happened, Kansuke attacks in fury at Nobukata Itagaki, one of Harunobu’s chief retainers. Though Kansuke is defeated, Itagaki gets impressed by his swordsmanship and tells Harunobu about the one-eyed man. Harunobu, who is also shocked by the cruel behavior of Nobutora, wants to see Kansuke. The two meet each other for the first time. Sensing Kansuke’s resentment against Nobutora, Harunobu persuades him to lay aside his grudge and hold ambition. Kansuke goes to Suruga on Itagaki’s order to spy into the Imagawa clan at internal strife. Kansuke informs Tadatane Ihara, his relative who is one of Imagawa’s main retainers, of the conspiracy against the clan leader. Ihara, however, tells Kansuke that the Imagawa leader as well as his brother has died mysteriously on the same day.
Kansuke is introduced to Jukeini, the mother of a potential successor to the late head of the Imagawa clan. Kansuke proposes the woman who has tremendous influence in the clan a plot to dispose of Fukushima, the betrayer who secretly communicates with Takeda Nobutora. Having no way to know that Jukeini’s son is working on amicable settlement with the Takada clan, Kansuke plans to take revenge on Nobutora for Mitsu when the head of the Takeda family comes to help Fukushima. Fukushima takes up arms against the Imagawa family but Takeda’s army does not turn up. Kansuke’s brother Sadahisa, who has been working under Fukushima, kills himself before Kansuke’s eyes.
Fukushima seeks refuge with Takeda’s retainer who introduced Fukushima to the head of the Takeda family. Nobutora kills both of the two. The conflict between Nobutora and his son Harunobu becomes more bitter after this. Meanwhile, Kansuke goes to see Jukeini’s son Yoshimoto, who now is the new head of Imagawa. Despite his achievements in disposing of Fukushima, Kansuke is refused to become a retainer of the clan. Kansuke’s hope to take revenge on Takeda with the help of Imagawa also disappears, as they are now in alliance. Kansuke departs for Sagami, the domain ruled by the Hojo clan, to look for a warlord to serve.
Kansuke is given a chance to talk to Ujiyasu Hojo, the head of the clan. However, Ujiyasu refuses to make Kansuke his retainer, sensing that Kansuke is driven by resentment against Takeda. Kansuke leaves Sagami and heads to Shinano. Meanwhile in Kai, Nobutora decides to conquer Shinano since the alliance with Imagawa enabled him to be off-guard about the southern border. In Shinano, Kansuke happens to meet again Heizo. Heizo is with his current master Sanada Yukitaka, who rules a small area of Shinano. The army of Takada leaves Kai and Harunobu also heads to Shinano for his maiden battle. At the news that Takeda’s troops are advancing on the Unnokuchi castle, Kansuke is sent to the castle as a messenger of Sanada.
The army of the Takeda clan besieges the Unnokuchi castle. Kansuke gives advice to the warlord of the castle and help him defend the castle from the 8000-person army. Harunobu Takeda has come to the battlefield for his maiden battle but cannot participate in the battle being deployed in the rear. After one month of struggle, Takeda Nobutora decides to retreat since his troops are about to run out of provisions and it has started to snow. The warlord of the Unnokuchi castle and his warriors are delighted to see the Takeda army leave. Kansuke advises them to keep vigilant but they start drinking believing that they have won. After a while, Harunobu returns with his 300-person troop.
Harunobu has taken the Unnokuchi castle by surprise. Kansuke appears in front of Harunobu, resigned to being killed. Harunobu puts his sword on Kansuke’s neck but leaves him alive, only declares that he has decapitated Kansuke. Three years later, Takeda allies with Suwa, a ruling clan of Shinano, and Harunobu’s younger sister Nene marries into the Suwa clan. Meanwhile, Nobutora openly shows his intention to expel Harunobu. Harunobu reveals to his right-hand man Itagaki that he is determined to oust the father from Kai.
Itagaki secretly works on persuading major Takeda retainers and the Imagawa clan to support Harunobu. Unaware of the conspiracy against him, Nobutora leaves Kai for Suruga invited by Yoshimoto Imagawa—the head of the Imagawa clan has chosen to side Harunobu and agreed to confine Nobutora in his domain forever. Kansuke, who has been in Suruga still masterless, is sent to bring Nobutora by order of Yoshimoto.
Harunobu declares in front of his retainers and his brother Nobushige that Nobutora is expelled. As the younger brother who was Nobutora’s favorite supports Harunobu’s decision, the retainers are united in aiding Harunobu as the clan’s new leader. Nobutora comes back from Suruga and sees Harunobu’s army is lined on the border. After a vain attempt to reenter Kai Domain, Nobutora realizes that he is expelled. Kansuke comes to take Nobutora to the capital of Suruga. On their way, the malice against Nobutora crosses on Kansuke’s mind. However, Kansuke’s anger dissipates when he sees Nobutora fall from a horse and show miserable senility.
Harunobu is now the leader of the Takeda clan. Kansuke has a masterless samurai attack Harunobu’s chief retainer Nobukata Itagaki and saves the retainer killing the samurai, for the purpose of becoming a retainer of Takeda. Itagaki sees through the plot but leaves Kansuke alive, remembering that Harunobu has once chosen to save Kansuke’s life. Hearing the incident from Itagaki, Harunobu calls up Kansuke in front of him and tells him to become his retainer, despite objections from other retainers.
Kansuke is challenged to a duel by the strongest retainer of the Takeda clan. Kansuke beats the samurai without an actual duel and makes Harunobu and the retainers appreciate his wisdom. Meanwhile, the second son of Harunobu loses his sight because of illness. Harunobu’s wife worries that this as an ominous sign of difficulties ahead brought by the one-eyed retainer. Harunobu takes no notice but her worry proves right—the powerful rival clan Uesugi starts invading Takeda’s land in Shinano.
Takeda’s territory in Shinano has been invaded by the Uesugi clan. Yorishige Suwa, Harunobu’s brother by marriage who has been allied with Takeda, makes peace with the Uesugi clan without consulting the head of the Takeda family. To design a plan to recover the land, Kansuke is sent to the Suwa region, where he first sees Yu, a daughter of Yorishige Suwa. Meanwhile in Kai, Harunobu chooses “furinkazan,” a quote from a military treatise written in ancient China, for new banners of his clan.
In April 1542, the first son is born to Yorishige Suwa and Nene, Harunobu’s sister. Kansuke proposes to Harunobu to secretly ally with a kin of the Suwa clan and launch a pincer movement, to regain the Suwa region without doing harm to Nene and the baby boy. Unexpectedly attacked by Harunobu, Yorishige Suwa is forced to be besieged in a castle with only a few retainers. Itagaki and Kansuke persuade the head of the Suwa family to surrender, saying Harunobu has no intention to destroy his family. Yorishige Suwa’s daughter Yu alone opposes taking Kansuke at his word.
Yorishige Suwa and Nene are sent to Kofu, Kai’s castle town, where the head of the Suwa clan is forced to kill himself. Kansuke goes to Suwa with Itagaki’s troops to make the remnants of the clan and the followers surrender. In the castle, Kansuke happens to find Yu. The princess has been refusing to follow her attendants’ persuasion to kill herself before she is insulted by the enemy. She yells out at Kansuke that she wants to be alive and see the world. Kansuke is instantly captivated by her noble beauty.
Kansuke decides to help Yu escape from captivity. Meanwhile, interested that Kansuke has saved the princess, Harunobu decides to take Yu as his own concubine, which is the only way to keep her alive. However, Yu feels hatred toward Harunobu, the very person who forced her father to kill himself. On her way, Yu is attacked by a masterless samurai and saved by Kansuke, who has come to bring her back, having learned of Harunobu’s decision. In order to turn Yu’s hatred from Harunobu toward himself, Kansuke tells her a lie that he, not Harunobu, sent the attacker.
Yu is brought to Kofu from Suwa and Harunobu declares that he will take Yu as his own concubine. The retainers bitterly oppose his idea. Only Kansuke sides with Harunobu, saying if a boy is born between the two and he becomes the head of the Suwa clan, Suwa’s people will swear loyalty the Takeda clan. Kansuke tries to persuade Yu but she rejects, saying she would rather kill herself than be a concubine of the man who caused death to her father. One of Harunobu’s retainers tries to compel Yu to commit suicide and Harunobu’s wife Sanjo flings harsh words at Yu.
Yu finally agrees to become Harunobu’s concubine. Harunobu holds a formal wedding ceremony for Yu to symbolize the ties between the two clans. Kansuke leaves for Shinano to devise a stratagem for further territorial expansion, believing that he has succeeded in prevailing on Yu to change her mind. However, Yu still carries a grudge against Harunobu and pulls a dagger on him.
In September 1543, Takeda’s army besieges Nagakubo Castle in Shinano. Harunobu decides to give Kansuke the position of Takeda’s military strategist, if he successfully captures the castle. With the help of the spy he has already sent into the enemy, Kansuke swiftly takes the castle. Meanwhile, Yu is in agony, torn apart between her affection and grudge toward Harunobu. Harunobu tells Kansuke to find out Yu’s true feelings.
Yu’s odd behavior sends ripples through the Takeda clan. Kansuke stands up for Yu and is accused by the senior retainers. Harunobu’s mother tries to admonish her but Yu just breaks down in tears. Harunobu decides to send Yu back to Suwa. Along the way to Suwa, Yu runs away. Kansuke manages to find her hiding in a small temple and hears her complicated feelings of love and resentment for Harunobu.
Yu becomes pregnant with Harunobu’s child. Kansuke is pleased as if it were his own. Meanwhile, Sessai, a military strategist of the Imagawa clan, visits Harunobu. Sessai asks him to send Takeda’s troops to Suruga based on the Takeda-Imagawa alliance, in order to help the Imagawa regain the territory that the Hojo clan has been occupying. Harunobu is skeptical about Imagawa’s true intensions. Kansuke is sent to Suruga to reconcile the Imagawa with the Hojo.
The Hojo clan is caught in a bind in their territory Musashi, as the strategic point Kawagoe Castle is put under siege by the army of Norimasa Uesugi. Kansuke goes to the castle, leading troops to help the Hojo clan, with another purpose in his mind—to persuade Yukitaka Sanada, who presently serves under the Uesugi clan, to be a retainer of the Takeda clan. Kansuke disguises himself and sneaks into Uesugi’s headquarters. Hearing from Kansuke that Uesugi’s troops are unvigilant and off guard, Ujiyasu Hojo decides to make a night assault against them.
Kansuke is wounded by gunfire in the night assault at Kawagoe Castle. He is saved by Yukitaka Sanada and stays at a temple in Kozuke, Uesugi’s territory, while the wound heals. Sanada makes up his mind to serve under Harunobu, the enemy of the Uesugi clan, but he faces stiff opposition from his wife and retainers. Meanwhile, Yu gives birth to a long-awaited baby boy, who is named Shiro. While in Echigo, the Nagao family seizes power and Kagetora Nagao, a younger brother of the head of the family, emerges as a powerful leader. Having returned to Kai and met baby Shiro, Kansuke finds a new purpose in life—aiding the son of Yu and Harunobu.
Kansuke devises a plan to make Shiro, the son of Yu and Harunobu, the next head of the Suwa clan. Toraoumaru, Yu’s half younger brother, has been regarded as the successor to the Suwa. In order to get rid of him, Kansuke goes to see Yoshimoto Imagawa and gets his approval to entrust Toraomaru to the Imagawa clan. Meanwhile, Harunobu enacts new laws for ruling his province.