The first time that Shao Cheng has killed a human being, it was because he has been pushed to hopelessness with no other choice but to either kill the person that was currently attacking his younger brother Chang Pei unless he hesitates and can only watch as the person he treats as a younger brother died right before his very eyes.
And with that concept alone, it has been an easy decision, Shao Cheng has made his choice and killed a person for the first time in his entire life.
As for a normal citizen of Earth, where it was a crime to take a human life, Shao Cheng has reacted the same way what a normal person responds regarding about taking away a person's life, and it was such a long time ago that Shao Cheng just felt it as, oh yeah…. I did that.
It was a lukewarm reaction whenever he thinks about it now, his heart has long been dead.