"Kingdom" is a historical anime series set during China's Warring States period, a time of intense conflict and political upheaval. The narrative centers on Xin, a war orphan from the Qin state who dreams of becoming the greatest general under the heavens. Alongside his childhood friend Piao, Xin trains relentlessly in martial arts, driven by a desire to rise above his humble beginnings. Piao is recruited into the royal palace, leaving Xin behind, but their paths diverge dramatically when Piao is mortally wounded in a coup. Before dying, Piao entrusts Xin with a mission to protect Ying Zheng, the young king of Qin, who is fighting to reclaim his throne from a usurper.

Xin's journey intertwines with Ying Zheng's struggle to unify China under his rule. The series explores the complexities of warfare, politics, and alliances as Xin rises through the ranks of the Qin military. His raw talent, unyielding determination, and loyalty to Ying Zheng earn him recognition, but his impulsive nature often puts him at odds with more seasoned commanders. Key figures in the story include Li Xin (Xin's official name after being recognized by the king), Diao, a skilled strategist and Xin's close ally, and Wang Qi, a legendary general who becomes Xin's mentor. The narrative also delves into the lives of rival states and their leaders, such as the ambitious and cunning Ri Boku of Zhao, who poses a significant threat to Qin's expansion.

The series balances large-scale battles with intimate character development, showcasing the brutal realities of war and the personal sacrifices required to achieve greatness. Themes of loyalty, ambition, and the cost of power are woven throughout the story, as Xin and Ying Zheng navigate the treacherous landscape of feudal China. The anime adapts the manga's epic scope, depicting pivotal historical events and battles with a focus on strategy, camaraderie, and the human spirit's resilience. Through its portrayal of historical figures and fictionalized accounts of their exploits, "Kingdom" offers a gripping exploration of a transformative era in Chinese history.