The cub figures it out

Finally, there was a light ripple in those beautiful eyes like his air of indifference had dissipated. It wasn't because the creature called him Ya Ya but the motive it spoke off. He knew Rui Fei was a loose cannon with an irrational outburst at times. This he knew from experience.

Even the first time they met Ji Yao was so terrified of him despite the fact that he was two years older than Rui Fei. Getting to know him he began to understand him better and from what he knew Rui Fei would behave irrationally if he is having an outburst episode or if someone threatens him.

But was this piece of knowledge worth killing someone over? It didn't make sense at all. The creature could sense his conflict so it said, "You don't know the kind of obsession that boy has over you. His love is the kind they call fatal attraction and look what he did. To remove anything that threatens your relationship with him he eliminated the competition."