I killed someone. It was the best thing I've ever done. This was what Ryoji Kirihara said to the police in " White Night Walk." Although this sentence itself was meaningless, it brought out the theme and plot of the entire novel. In the novel, Kirihara Ryoji and Yukiho Karasawa were mutually dependent. They planned everything together, including the murder and covering up the crime. And the 'I killed' in this sentence meant that they had transcended their personal dependence and reached a state of mutual domination. Therefore, the meaning of this sentence was to reveal their close relationship and their determination to cover up their crimes.