First of all, if Cai Yang didn't kill him, he was also killed.
Cai Yang is a general under Cao Cao. Later, Guan Yu was killed by Guan Yu's backhand. When Cao Cao attacked Xuzhou Liu Bei, Liu Bei fled with Zhang Fei, but Guan Yu and Liu Bei's two wives were captured by Cao Cao, and Guan Yu had to surrender. After Guan Yu surrendered, Liu Bei was still bitter and bent on finding Liu Bei's way out. Later, Guan Yu was ordered to attack Baima. Guan Yu beheaded Yan Liang and helped Cao Cao defeat Yuan Jun in Yanjin. It was at this time that Guan Yu discovered the sight of Liu Bei.
After Guan Yu came back, he wrote a letter to Cao Cao and left with his two sisters-in-law. Guan Yu had a hard journey. Guan Yu went through five customs and beheaded six generals, and later came to the ancient city, where he actually met Zhang Fei. Guan Yu was very happy to see Zhang Fei. He just wants to talk to Zhang Fei. As a result, Zhang Fei came to fuck himself. Guan Yu asked why. It turned out that Zhang Fei thought Guan Yu had surrendered to Cao Cao and defected. Guan Yu explained that Zhang Fei would not listen.
At this time, Cai Yang led an army of one hundred and fifty thousand to pursue Guan Yu from Xudu. Guan Yu himself was not convinced of killing his nephew Chyi Chin. Guan Yu had to face Cai Yang and was killed by Guan Yu in the blink of an eye. Guan Yu killed Cai Yang, and Zhang Fei began to call Guan Yu a good brother.
Second, in the official history, Cai Yang was killed by Liu Bei.
Of course, all the above are the sayings of the romance of the Three Kingdoms. Romance is just a literary novel, so it can't be taken seriously. But there is a Cai Yang in history. He is indeed a general under Cao Cao. At that time, Liu Bei and Gong Dou of Runa prepared to take refuge in Yuan Shao to kill Cao Cao. When Cao Cao heard this, he sent Cai Yang to kill the two men. As a result, Cai was defeated and finally killed by Liu Bei. This is clearly recorded in the History of the Three Kingdoms, so it is false for Cai Yang to pursue Guan Yu thousands of miles away. This is just a fictional story made up by Luo Guanzhong to exaggerate Guan Yu.