It is about the idea of possibilities. Parallel worlds. They describe it as one bubble splitting in two, circling each other as they ascend towards the same place. The idea has been touched on a number of times. What would my life have been if I had turned right instead of left? Who would I have met and who wouldn’t I have met?
These films are separate, but like two bubbles they circle around each other. They present as two possibilites for the same boy.
The impact is more in the thought provoking nature rather than illiciting deep feeling. The deeper feeling was sacrificed to make room for the establishment of the science. And while there is debate on which order to watch the films in, there is only one order that makes sense and allows for the story to build on itself. Similar to the way that there is only one order to watch the Star Wars films to gain the most fulfilling experience.
In the same vein as Your Name, these films have that “what if” flavor. The desperate and driving need to bend the laws of physics to save someone you love.