Under the huge setting of guarding the earth, a large part of this story is still about the emotions of William and Rita. This emotion is not the traditional Hollywood structure of one party protecting the other, but the ambiguous sentiment that fights side by side. What's more important is that William's ability has gradually deepened his understanding of Rita, but Rita can only stay where he is. What hinders them is Rita's previous emotions, which was touched by the film. That person who also possessed William's ability, the final death made Rita become obsessed with fighting and her heart was locked.
The description of the two people's emotional lines in the film is not deliberate, but only uses small details like William knows that Rita likes coffee and three parts of sugar from time to time. In the end, it is inevitable to step into the old Hollywood routines, but the joy of becoming the most familiar stranger can also be regarded as a satisfactory explanation for the audience.
