There were two possible reasons Ku He wanted to kill Xiao En. The first possibility was that Xiao En knew Ku He's unspeakable secret. Back then, Ku He was so hungry that he wanted to feed on humans, and Xiao En had witnessed that scene with his own eyes. In order to protect his reputation, Ku He did not want Xiao En to reveal this secret, so he decided to kill Xiao En. The other possibility was that when Xiao En and Ku He were searching for the temple together, Ku He had obtained a martial arts manual from Ye Qingmei, which had allowed him to break through the boundary and become a Great Grandmaster. Ku He was grateful to Ye Qingmei and knelt down to her. If Ye Qingmei had not revealed this secret, Ku He might not have killed Xiao En. However, the specific reason might need to be further watched to understand.
The reason why Destiny killed her clone was to help her brother change his fate. Tianming was the strongest of the four avatars of the protagonist Ye Xuan's sister, Qing 'er. In her previous life, Qing 'er's brother gave her the last steamed bun to eat, and he starved to death. Therefore, the destiny left behind a strong obsession to find his brother and protect him. Tianming was extremely powerful. She could kill people with a single sword strike. In order to help her brother defy the heavens and change fate, she carried out a large number of massacres and even destroyed an entire planet with a single sword strike. However, the other two clones did not agree with her defying the law and thought that she had killed too many people. Thus, Tianming decided to kill these two clones. In short, the reason why Destiny killed the clone was to find her brother and protect him, as well as to help her brother change his fate.
There were two possible reasons Ku He wanted to kill Xiao En. The first possibility was that Xiao En knew Ku He's unspeakable secret. Back then, Ku He was so hungry that he wanted to feed on humans, and Xiao En had witnessed that scene with his own eyes. In order to protect his reputation, Ku He did not want Xiao En to reveal this secret, so he decided to kill Xiao En. The second possibility was that Ku He wanted to keep the temple a secret and didn't want anyone to know about its existence. Xiao En and Ku He had rescued Ye Qingmei together, so Xiao En also knew the secret of the temple. Ku He was worried that Xiao En would reveal the secret of the temple, so he decided to kill Xiao En. These are the possible reasons based on the search results provided. The specific plot and details may require further reading to obtain a more accurate answer.