During an excavation on the seashore of Hakata, Shun Gaue (the associate professor of the department of archaeology at the University of Kitakyushu) discovers a Western sword dating back to the Kamakura period. This sword was the exact match to a dagger Shun had seen his grandparent’s storage house when he was a child. 

1276 A.D Edward Gawain, a British Knight who participated in the Crusades finds his ship drifting out at sea far from the shores of Jerusalem. Among the 50 men abord his ship is his best friend since childhood, Alan, his close confidant and Saracen merchant, Zafir, and the ship’s captain Thomas. Once they pass India and Malay, their ship eventually runs aground on the shores of Hakata, Nippon (the modern-day Japan). Once ashore, Edward and his men are captured and taken to a samurai named Adachi Morimune. Morimune was the commander tasked with hunting down the remnants of the Mongolian Army that had attacked Nippon two years prior. Using their own merchant companions, Zafir and Xie WangSheng, as translators, Edward and Morimune learn to communicate. 

During the journey to Hakata, Edward and Morimune’s party is ambushed by a Mongolian scouting party. Edward helps them secure victory and saves Morimune’s life when he was shot by a poison arrow. Such a heroic act opened Morimune’s heart to Edward, and Edward and his men, in turn, open their hearts to Japanese culture. Learning more about this unknown civilization so different from their own. They find themselves filling with rage as they hear about the atrocities the Mongolians inflicted village after village in Hakata. Yet, Edward found it mysterious that this island country was able to drive the Mongolians off its shores. The same Mongolian army that had enough force to conquer the entire world. He observed both side’s weapons and battle strategies and began making an analysis. Edward grasped that Nippon’s bow, arrows, and armor were surprising strong. Yet, as the same time, had weak points.

Edward and his party eventually follow Morimune to Kamakura. There, they encounter Nichiren who was preaching to the masses. Nichiren had gain a large following after predicting the invasion of the Mongolians in the previous war. Residing in Kamakura is also Tokimune (a regent of the shogunate) who was burdened with responsibility of compensating the samurai who fought in the last war and building their defenses against the threat of a second invasion. Tokimune finds great interest in Edward, who fights for the sake of faith. Henceforth, Tokimune calls upon Edward to talk of foreign weapons and tactics, as well as of faith. Within those conversations, Tokimune learns of the trebuchet that Edward brought with him from Hakata, and willfully burns it. 

A year passes and Edward and his party have grown accustomed to Japan. However, Edward learns one of his subordinates, Michael, drunkenly raped a woman and killed her and her family. Tokimune leaves the punishment for such a crime in Edward’s hands. Edward makes the decision that Michael must die for his actions. Despite opposing to this decision, Alan carries out the execution in Edward’s stead, to prevent the sullying of Edward’s hands. 
After a deep conversation on faith with Tokimune, Edward begins to worry that about the salvation for the souls of those who kill during war. One night a woman named Haruno is sent to Edward’s room. He sleeps with her and takes her on as his lover. His Japanese begins to improve even more. 
Invited by Morimune, Edward accompanies Tokimune out hunting. During the hunt, Tokimune’s uncle sends troops to assassinate Tokimune. Edward saves him using impressive defensive strategies. In thanks, Tokimune gifts Edward his favorite horse, Hayate (Swift Wind). It is around this time that Edward realizes he wishes to protect Nippon, the homeland of his beloved Haruno. 

Edward learns of the war preparations the Mongolian Army has begun through the information network that Zafir had been collecting. The samurai are astonished at the immense scale of the Mongolian Army. Edward begins to break down the possible invasion routes in the Hakata Bay, the structure of bulwark barriers, the command structure, and so on. He shows Tokimune the benefits of a unified army and demands this to be introduce to the Japanese Army. Tokimune acknowledges the effectiveness of this strategy and entrusts Edward with training the samurai, despite the surrounding opposition. He trains not only the samurai, but also the local farmers to become archers. Before they know it those in their party from Europe begin to have families and children. Surprising everyone.  
Edward requests of Tokimune to change the system of samurai compensation for the sake of unifying their army, but Tokimune cannot change this traditional mindset. However, Zafir spreads rumors of the cruelty and barbarity of the Mongolian Army. The worry takes seed, and the samurai change their stance on the issue. Doing whatever they can for the sake of victory. Tokimune requests Edward completely take command over the army heading for Hakata. His new subordinates follow him willingly. 

Once Edward and his men arrive in Hakata, they prepare a large number of bows and arrows for Morimune and repair the trebuchet. As well as, teaching the local farmers how to operate it. At first the farmers refused to learn how to use this strange new weapon, but eventually they changed their minds. It was also difficult to try and repair the trebuchet, however thanks to the collaboration with a carpenter named Sousuke, the trebuchet performed even better than before. 
At long last, the Mongolians began the onslaught of their invasion. Completely decimating Iki Island in their wake. Edward’s strategies began failing left and right as samurai rushed headfirst into battle, despite them being ordered not to. Even with these failures, Edward succeeded in defending off the siege, but the damage to Nippon was great. Edward also implemented ruthless western tactics. He would throw decomposing corpses into fresh water sources, to run the Mongolian’s resources dry. The villages they expected the Mongolian Army to use as a base would be burned down beforehand. The village women would weep as they were forced to burn down their own homes.  
 
The following day, unable to prevent an all-out attack from the Mongolian Army, Edward and his men ordered the resisting farmers to retreat. The samurai had already retreated to the Dazaifu governmental office, and Morimune and Edward had stayed behind to aid the farmers. They clashed with the Mongolian Army and narrowly won the battle, but lost Alan in the process. Risking the danger Haruno appeared before Edward that night. She told him that Xie WangSheng had prepared an escape route for them. 
Despite even Thomas telling him to escape by boat, Edward chose to stay behind and fight to protect the people of his new home. As the final battle with the Mongolian army drew near, Edward ordered Enrico to give his dagger and cross to Haruno. Before Enrico could even return, Edward charged on the Mongolian Army. 
The Mongolian Army then disappeared. 
Tokimune tried to find Edward’s whereabouts, but in the end, he was never able to find him. He then erased all records of Edward and his men from Europe’s existence.
 

Present day.
After finishing a lecture Professor Gaue returns to his office. In his hand on the dagger Edward left behind for Haruno. 

Characters

Edward Gawain : A Knight of England.
Alan Percy : Edward's attendant and best friend since childhood.
Zafir : Saracen merchant. Purchased as a slave by Edward in Jerusalem. 
Thomas : Hailing from Genova. Captain of “Blu Oceano”.
Enrico : Subordinate in Thomas and the sailing master of the “Blu Oceano”

Hojo Tokimune : Regent of the Shogunate Nippon Government.
Adachi Yasumori : Tokimune’s closest attendant.
Adachi Morimune : Son of Yasumori. Stationed in Hakata, and the first person Edward encounters in Nippon.
Takakura Haruno : Nippon courtesan. 
Xie WangSheng (Sha Ohsho) : Trading merchant person in Hakata.
Nichiren : The priest who spreads the Lotus Sutra.

Gaue Shun : The assistant professor of the department of the Kitakyushu University department-of-literature archaeology.