When he saved her that year, he used a trick to block a knife for her. In the night, she put on her armor and clasped her fists at him and said, "I can't repay my kindness today. From now on, you are my brother. My eldest brother's business is my business."
Machiavellian plots, repeated over and over again, he climbed up step by step, and finally plotted against the person he cared about.
PS: The male protagonist is a villain, and the female protagonist is a Jianghu noob.