Orphaned by war, Xin Kento Yamazaki is sold as a slave to a small village, where he befriends Piao Ryō Yoshizawa, another slave. Growing up, Xin and Piao train together, dreaming of escaping their low status and eventually becoming great generals. Chang Wen Jun Masahiro Takashima visits their village in search of soldiers to aid the king Ying Zheng, but he will only accept Piao. Some time later a mortally wounded Piao appears at Xin's house, warning him that Ying Zheng's brother, Cheng Jiao Kanata Hongô, has started a power struggle and urging him to go to a point marked on a map he gives him. Xin sets off immediately, not knowing that his village has been set on fire and all the villagers murdered by Cheng Jiao's army.
At the meet-up point, Xin finds Ying Zheng, the king of Qin, where they are ambushed by a skilled Shukyou assassin. Xin realizes that Piao was accepted into the army to serve as Ying Zheng's double due to his bearing a resemblance to the king. Xin kills the assassin and the two escape through a mountain path with help from He Liao Diao Kanna Hashimoto, a mountain tribe child who had accompanied the bandits that had previously ambushed Xin. As the three reach the bamboo forest, they are attacked by another assassin. Despite blaming Ying Zheng for Piao's death, Xin defeats the assassin but is poisoned by one of his darts. The three take refuge at an ancient summer resort to help Xin recuperate, while Xin learns that Piao had voluntarily sacrificed himself to serve Ying Zheng, and about Ying Zheng's bitter rivalry with Cheng Jiao, his brother.
Ying Zheng's remaining army finally arrive at the summer resort, including Chang Wen Jun, who was previously assumed to have been killed by General Wang Qi. The army is outnumbered by Cheng Jiao's army of 80,000 soldiers, while Ying Zheng admits that Lü Buwei, the only person who can outmatch him, is also after the throne. Ying Zheng chooses to seek out help from the Mountain Tribe, a former ally of the Qin royal family that had been betrayed 400 years ago. As they rise into the mountains, they are captured by the Mountain Tribe and brought forth to the chieftain, Yang Duan He Masami Nagasawa. Yang Duan He orders Xin to be beheaded to test Ying Zheng's loyalty, but Xin's dedication to Ying Zheng's goal and mannerisms impress her, after which she announces that the Mountain Tribe will be affiliated with the Qin royalty again.
Ying Zheng's army arrives at the royal palace disguised as part of the Mountain Tribe, under the pretense of helping Cheng Jiao fight against Lü Buwei. Jie Shi Shinnosuke Abe, Cheng Jiao's advisor, allows only 50 people inside, and 10 of them to meet with Cheng Jiao. Just inside the gates, Ying Zheng initiates an attack, while Xin, Diao, and Bi use the underground passageway to reach the throne room and assassinate Cheng Jiao. Xin's group is intercepted by Zuo Ci, Ying Zheng's former general, who sends Lang Kai the Executioner after them. Xin kills Lang Kai with the help of the Mountain Tribe, and when they reach Cheng Jiao's room, Zuo Ci defeats Xin's group. Just when it seems Zuo Ci will succeed in killing the exhausted Xin, Xin's memory of Piao and belief in his own dreams brings him renewed strength and he kills Zuo Ci. Cheng Jiao's council flees, but Diao gouges out Jie Shi's eye with a dart and is stabbed by him before he dies. While Diao is safe thanks to wearing armor, Cheng Jiao uses their distraction to escape.
In the courtyard, Cheng Jiao confronts Ying Zheng, but is easily defeated. Ying Zheng spares Cheng Jiao, but beats him up to punish him for the suffering he caused. General Wang Qi appears in the courtyard where he asks Ying Zheng what he will do as king and threatens to behead him if he does not provide a satisfactory answer. Ying Zheng vows to unite China under the Warring States period, even using force as a means to ensure that there would be peace in the future. Satisfied with his answer, General Wang Qi allies with Ying Zheng and orders Cheng Jiao's remaining army to retreat. With the battle won, Xin revels in the glory of making both his and Piao's dreams come true.
