How does the Confucian notion of 'righteousness' or 'duty' (義) shape the dynamic between Guan Yu and Cao Cao? What archetypal qualities are shared by both Guan Yu and Cao Cao, and what qualities set the two characters apart from one another?

Romance of the Three Kingdoms is a 14th century historical novel written by Chinese author Luo Guanzhong. It is considered to be a perfect mix between legend, myth, and history, and it is one of the Four Great Novels of China. Because of its popularity, the novel influenced many other literary works, and many movies, TV shows, plays, radio programs and games are based on its beloved and captivating narrative.
The novel describes the end of the Han dynasty, and the start of the Three Kingdoms period, which began with the founding of the state of Cao Wei in 220, and the conquest of the state of Eastern Wu by the Western Jin dynasty, in 280. It focuses on three main heroes: Liu Bei, Guan Yu, and Zhang Fei; and one main villain – Cao Cao.
Guan Yu, a.k.a Guan Gong, was a true personification of a real hero. Even if there are many talented and mighty warriors in Romance of the Three Kingdoms, Guan Yu was still considered one of the best and most popular, and many worshiped him as the “God of War.” He was over six feet tall, with a long and luscious beard, which earned him the nickname Lord Beautiful Beard. His weapon of choice was a long and heavy sword named Green Dragon Crescent Blade. While his companions and colleagues were not very academically inclined, Guan Yu was a literate, educated man who enjoyed reading, especially Confucius.
In order to protect his lord Liu Bei’s family, Guan Yu allowed himself to be captured by Cao Cao. Cao Cao, who had long admired Guan Yu as a warrior, tried to win him over to his side by offering him various goods such as gold, fast horses, and noble titles. However, Guan Yu escaped and returned Liu Bei’s family back to him. In the novel, Guan Yu's name is a synonym for loyalty, honor, righteousness, benevolence, selflessness, and duty.
Thus, according to many, he was the real embodiment of Yi. Essentially, it is the concept of Yi that shapes the dynamic between Guan Yu and Cao Cao. In Confucianism, Yi literally means justice and righteousness. It is a notion that enables people (especially leaders) to be good, moral, ethical and benevolent.
Unlike Guan Yu, Cao Cao was a man who had very little Yi. He was of a smaller stature, with narrowed eyes and a long beard. He was ruthless, merciless, pragmatic, and sometimes even scared and paranoid. He lived by one philosophy: He’d rather wrong the world, than let the world wrong him. However, he is also described as generous, and sometimes even an honorable man, which were some of the qualities he shared with Guan Yu. He didn’t really believe in the notion of loyalty and righteousness, as he believed that loyalty can always be gained if one treats people well enough. This is also one of the characteristics he shared with Guan Yu, as the general also believed that loyalty is conditional.
Aside from being a talented warrior and general, Cao Cao was also an excellent poet. His grandfather was a eunuch, which gave him a lower social status than Liu Bei, for instance, who had imperial lineage. However, he didn’t let this affect his determination and his will. He admired Guan Yu, because in a way he saw an ideal version of himself in the general. Guan Yu never forgot Cao Cao’s generosity. Thus, when Guan Yu faced the defeated Cao Cao who lost the battle of the Red Cliff, he let him go.
Romance of the Three Kingdoms carries a powerful message. Guanzhong believed that humans cannot control their destiny. Instead, he believed that our fate is predetermined, and it is, essentially, written in the stars. We cannot alter what was already written for us; we can only try to be kind, selfless, righteous, hard-working, and honorable, so that we can leave a legacy that will be remembered forever.