In the epic Romance of the Three Kings, many Confucian concepts are explored and presented in various examples. One of the recurring concepts is Yi, which is "justice or righteousness." The idea of doing what is right is exemplified by Lord Guan Yu and Cao Cao's complex relationship.
Lord Guan Yu is loyal to his sworn brother, Liu Pei, but serves Cao Cao—a cruel and Machiavellian warlord—for a brief period. In order to repay Cao Cao's kindness, Lord Guan Yu slays a bitter rival of Cao Cao. When Lord Guan Yu decides to return to Liu Pei, Cao Cao's forces want to pursue him.
However, Cao Cao stops them and states that Lord Guan Yu is a righteous warrior being dutiful and loyal to his sworn brother, Liu Pei. Both men display the concept of righteousness in their actions toward each other.