What is the origin of the imperial seal in Romance of the Three Kingdoms?

In Romance of the Three Kingdoms, Yuan Shu is an unexpected imperial seal, and he is the king of Huainan.

During the Three Kingdoms period, Yuan Shu was famous for his crusade against Dong Zhuo. Later, Yuan Shu opposed Yuan Shao, but was defeated by Yuan Shao and Cao Cao. Later, Yuan Shu won the imperial edict in the second year of Jian 'an, but Yuan Shu had no way to govern the country, which made the people in Jianghuai area miserable at that time. Yuan Shu, who was alienated from others, was finally forced by Lu Bu and Cao Cao to vomit blood and die.

As for Huainan's hegemony, Yuan Shu said that no one dared to say the second. First, Yuan Shu, with 300,000 troops in hand, once played a horse with Sun Ce for the sake of the imperial seal. Yuan Shu felt that he was one step away from his dream of becoming an emperor. When the civil and military officials who protected Emperor Xian of Han Dynasty were defeated, Yuan Shu felt that the time was ripe. In the second year of Jian 'an, Yuan Shu proclaimed himself emperor in Shouchun and built a horn bell.

But it didn't last long. After Yuan Shu proclaimed himself emperor, he lived in luxury. There were hundreds of concubines in the harem, but the soldiers in the army were hungry and cold. Under his corrupt rule, the Jianghuai area changed from rich to bitter. Yuan Shu himself vomited blood and died after leaving his family behind.