A group of exiles are being taken by boat to Tsushima Island when they are caught in a savage storm. They plead for their bonds to be removed, but then take over the boat and commence fighting among themselves. Kuchii Jinzaburō, saves Chō Minpuku, a fellow exile, and then fights to defend himself from other prisoners. He frees the pirate Onitakemaru who raises the mast and helps sail the boat towards Tsushima Island. On arrival, the boatload of exiles and crew are warmly welcomed by Princess Teruhi, but then find they are asked to defend the island against the Mukuri (Mongols). Pressed by Jinzaburō, Teruhi tells them that she had asked the Dazaifu magistrate to send able-bodied prisoners to support her. That night, masked intruders attack and the prisoners free themselves. Kaitani Gontarō tries to fight them off, but the princess is captured. Onitakemaru and then Jinzaburō intervene, Jinzaburō killing all but one of the masked attackers and rescuing Teruhi. The next day, overlooking the slain, Teruhi is distraught at the carnage of war, but Jinzaburō tells her it is just a skirmish. She promises him a reward and asks for his aid. The next day, October 3 of the 11th year of the Bunmei era, Kano reports that a fleet of Mukuri ships are heading for Tsushima Island.

Teruhi invites Jinzaburō to a strategy conference, but is ejected by Sō Sukekuni after disagreeing with his assumption that the Mongols will pass Tsushima. He meets Shōni Kagasuke, dressed as a monk, who asks him to help defend Tsushima for 7 days while he readies reinforcements, presenting him with the favourite sword of Minamato no Yoshitsune. The next day, the Mongol fleet lands at Sasu Bay and Sō Sukekuni rides overnight with his forces to meet them. Sō Sukekuni orders Jinzaburō to the rear to protect Teruhi and prepares to repel the invaders. After withstanding volleys of arrows from the advance party of Mongols, Sō Sukekuni's men push them back to the shore where they find the Sasu villagers slaughtered. However after the initial victory, the force of 200 soldiers and 80 horses are assaulted by explosives fired from the ships and are overwhelmed by a larger force of 1,000 Goryeo soldiers and Sō Sukekuni is killed.

As the surviving Tsushima soldiers retreat, they are confronted by Jinzaburō wearing Tsushima armor who tells them to stop and fight the pursuing Goryeo soldiers. They are reluctant to follow an exile, but when Jinzaburō and some of the other exiles attack the pursuers, the Tsushima soldiers turn and follow them. Obusama Saburō, Shiraishi Kazuhisa and Hitari support the attack, forcing the invaders to fall back and regroup. Jinzaburō insists on pursuing them, however Abiru Yajirō urges caution and does not follow. Meanwhile, the exiles and supporting soldiers are surrounded by the more numerous invading forces, but led by Jinzaburō they manage to break through to their headquarters, slaying their general and his men before returning with the heads of the slain Sō Sukekuni and Umajirō. Teruhi entreats the villagers of Sasu to join them in defending the capital, but Jinzaburō insists on a night raid on the invaders. Abiru Yajirō disagrees and returns to the capital. Using Amushi as a lookout Jinzaburō prepares to lead them on a hit and run raid against the small invading force by moonlight. However they are betrayed by two Sasu villagers, and when villager Ginshichi tries to kill Jinzaburō from behind, Teruhi distracts him and is cut by his sword.

Jinzaburō kills Ginshichi and sends the wounded Teruhi back. Then, throwing caution to the wind, he leads the night attack on the now prepared Goryeo forces. Onitakemaru opens a path through their defenses, but the Goryeo Commander, Kim Bang-gyeong and the Mongol vice-Marshal Liu Fuheng are unperturbed, suspecting they are under attack by only a small Tsushima force. Having caused enough fear and damage, Jinzaburō orders a retreat, even after hearing the cries of the Sasu village women and children held captive. Suddenly, a small Toibarai force assaults the Goryeo soldiers with arrows, giving Jinzaburō's men an opportunity to rescue the villagers. Before they retreat, the Toibarai commander, Nagamine Hangan, tells Jinzaburō they are acting under orders from Japan. Meanwhile, Liu Fuheng wants to capture the fighter who slayed their general days earlier and decides to pursue Jinzaburō himself. He first encounters Onitakemaru, then is confronted by Jinzaburō, but is prevented from chasing them into the night by his men. The Mongol army Marshal, Hindin, is advised by his priest that they should leave for Hakata in 7 days, so Hindin decides to continue his invasion of Tsushima. Meanwhile, while returning to the capital, Jinzaburō supports Ginshichi's son Sasamauru from being bullied by the other Sasu survivors.

Returning to the capital Teruhi and Jinzaburō's group see the city the distance, in flames after an attack by the Mongols. They find some survivors led by Abiru Yajirō who says that other survivors are scattered throughout the hills. Before they can devise a plan, they are detected by a small group of Mongol scouts and Teruhi fires arrows at them in frustration and anger. Amushi then sees a large force marching towards them, who are led by the Mongul Mingghan Commander, Uriyan Edei. As the survivors head for shelter at Aso Bay, an old woman inspires some soldiers to stop and fight a rearguard action along with the exiles. On the narrow trail, Jinzaburō plans a strategic defense based on his fighting experience. Jinzaburō tells Abiru of his time in Kamakura with Nagoe Tokaiki of the Hōjō clan who told him that playing shogi and war were the same, and to never lose sight of the big picture. He also learned that if you lay down your sword you can never win. Just then, the monguls attack with explosives and charge through the blinding smoke. However, the defending forces led by Jinzaburō recover and decimate the attackers with arrows. Following this experience, Abiru finds newfound resolve and promises to support Jinzaburō.

Mongul Mingghan Commander Uriyan Edei proposes that they use their shintenrai (震天雷 "heaven-shaking thunder") hand cannons against the defenders to reduce casualties among his men. From a distance, Teruhi and Harari try to shoot him with their bows but fail. Jinzaburō and Abiru's group prepare to withdraw, but suddenly Chinese soldiers ,in the Mongol army, shoot Abiru with a shintenrai, killing him. Meanwhile, the Goryeo troops from Sasu begin to approach from the west. Jinzaburō hopes the two different armies will be confused when they meet in the fading light. When the Goryeo and Mongols meet they start fighting over valuables left behind by the fleeing islanders, allowing the defenders to escape north. That night, Teruhi and Jinzaburō are approached by an old man who is with the Toibarai. Jinzaburō follows him through the night, and at dawn finds himself on the peak of Mt. Shiratake and is introduced to Tokihito, known as the Emperor Antoku.

In a flashback, Emperor Antoku gives the High General of the Genji Forces, Minamoto-no-Kurō-Yoshitune a short sword. Back in the present, the Emperor recognizes the same sword carried by Jinzaburō. Teruhi then arrives and is welcomed by her great-grandfather the Emperor who gives her a message for the Magistrate Nagamine of the Toibarai - to protect Sasu and the capital. Teruhi swears to protect the island, but her Sō clan are unhappy about relying on the Toibarai. When the survivors arrive at Aso Bay, they find the Toibarai women abalone divers have led a small seaborne advance party of Mongols into a trap, killing them all. They also discover that the invaders are composed of many different groups, and these are Jurchen. Teruhi gives Nagamine the message from the Emperor, and he agrees to help her, taking the Sō survivors to their castle, Kanatanoki. First built 600 years earlier, the Sō discover the castle is well-fortified and supplied, however Jinzaburō declares that it is too big to defend with the limited forces they have.

The exile Obusuma Saburō tells fellow exile Shiraishi that they have no responsibility to defend Tsushima. Meanwhile Nagamine tells Jinzaburō that the Toibarai will never abandon their castle fortress even though they lack numbers to adequately defend it. After sparring with some Toibarai soldiers who challenge him, Jinzaburō promises Nagamine that he will help with their defense. Meanwhile Obusuma reveals to Shiraishi that he has a pass enabling him to safely contact the Mongols, saying he's happy to serve whoever rewards his effort. Shiraishi refuses to join him, but he kills Obusuma whom he distrusts, and takes the pass himself. In the Mongol camp, Obusuma Uriyan Edei's commanders are frustrated of the disappearance of the Japanese islanders, but Uriyan Edei only agrees to pursue them if he has verified information about their location. At the Chikuzen Dazaifu Magistrate Fortress on the mainland, they prepare to reinforce the Tsushima defenders who are hoping for reinforcements, but doubt that they will arrive in time. Meanwhile, Shiraishi approaches the Mongols himself and offers information about a weakness in the castle fortification. He later returns to the castle with a dead boar to allay suspicions about his disappearance.