Cang Lang chose Ye Tianchen for a reason when he selected him to guarantee the mission to Yang Yi's leadership. There were two conditions that only Ye Tianchen fully met.
First, Ye Tianchen was once a special forces soldier and is now retired, simply a citizen of China. His actions do not represent the country's will.
Second, Ye Tianchen possesses strong skills that are unfathomable. Moreover, this guy tends to be violent. He doesn't look for trouble, but he's certainly not afraid of it. Anyone who crosses him will have to contend with his fists, even if they are the Heavenly King himself.
As for Ye Tianchen, Cang Lang sometimes envied the kid. He could curse and fight whenever he wanted, never picking a fight but always ready to engage anyone who troubled him with a thorough beating.