Setsu asked Cain if she's ok to go hang out with those guys. When they heard that he was her brother, they are relaxed because brothers usually are easy to let their sisters go.
Cain ignores them and said let's go to Setsu. One of the guys went and punch Cain but he dodged him. The guy became serious and began "fight" with Cain. Now Setsu is afraid that Cain's identity will be revealed. As the fight goes on, rest of the guys began to attack from behind and Setsu warned him, and stopped one of them. He said don't disturb him. With that Cain began to fight the guy and he went unconscious. They, including Setsu, are all afraid.