Yan Yu was 18 or 19, his stepmother's child from a previous marriage had died due to a severe illness. It was unclear whether it was due to the loss of his son, but his stepmother began to act erratically.
He became his father's only son, and his treatment at home began to gradually improve.
For some unknown reason, he fell out with Chu Guodong, who soon enlisted in the military service.
It was certain that Yan Yu's involvement with the drug dealers was discovered by Chu Guodong when he accidentally saw Yan Yu interacting with a person involved in a previous mission. This person was the one who had initially noticed the drug trafficking organization's activities and had proposed that their squad be sent out to carry out the mission.
However, based on this alone, Chu Guodong wouldn't have been aware of Yan Yu's involvement. After all, it was entirely normal for everyone who lived in the same compound to know a few mutual acquaintances.
