Although he has yet to make a frontal appearance in the manga, his silhouette shows that he was a man of average built with short, brown hair. He was dressed in a royal mantle and wore the Qin official's head decorations.
Boku Kou was one of the rare benevolent lords of Chinese history. He loved people from the bottom of his heart and showed the same level of respect be it a noble or an enemy prisoner.
He was the reigning Qin monarch from 4 centuries ago. After a battle, Boku Kou's warhorse was killed and eaten by some savage tribe in the mountains. The king, instead of punishing the savages, he offered some liquor that tastes good with horse meat. With that act of benign, he gained their respect and managed to form an alliance. As thanks, the mountain people built a summer getaway for him.
After a 13 year reign, the neighboring state of Jin was experiencing a famine(widespread scarcity of food). Although Jin was the enemy, Boku Kou pitied the peasants. He lent them a vast amount of food; an unbroken chain of boats and carts from Qin carrying food. Later referred to as the "Fan Zhou Zhi Yi". However, when it was Qin that was suffering from a famine, Jin takes advantage of this and invades Qin.
Boku Kou was so enraged that he led the army himself against Jin. In the initial stage, Qin fought on equal grounds with Jin, but the scarcity in food made Qin suffer from hunger and eventually from fatigue. Jin gained the upper hand and Boku Kou was surrounded. However, 300 mountain people came to Qin aid in order to repay the favor of wine and horse meat. Not only did they route the Jin forces, but the also managed to capture the enemy king and bring him before Boku Kou.
This is later called the story of "Horse and Liquor War". After his death, he would be buried at the Summer Getaway constructed for him by the mountain people. Unfortunately, his alliance with them was broken by Qin after his death and wouldn't be revived until 4 centuries later under his descendant, Ei Sei, and the young king of the Mountain tribes, Yo Tan Wa.
Boku Kou takes no part in the story, as he passed away many years before the start of the current era.
His skills as a leader and his love for humans lead him to establish a cordial relation with the Mountain People which was very crucial in future battles.
- Boku Kou gave birth to the "Horse and Liquor" legend.
- Besides being mentioned in Chapter 16 in the main story, he is also portrayed in the Horse and Liquor for 300 Soldiers one-shot that Hara Yasuhisa had written before Kingdom was serialized. The one-shot also named his favorite horses by the names, Qun and Lun, while depicting Yo Tan Wa's ancestor.