Nietzsche
I don't know how many people noticed that the father picked up an English copy of Nietzsche's Thus Spoke Zarathustra, and flashed it at the camera just before giving his speech to the daughter (before leaving Kyoto).
I usually hate philosophizing a film beyond what the director CLEARLY implicates. I hate it when I hear some idiot drone about how the film was communicating Marxist ideals against capitalism (such as happened in the message board for "Akarui mirai"). Often, people are merely reading their own bias and worldview into the movie and metaphoricalize waaaay too much. However, I make an exception for this because it is a very odd book to simply place in the film at the moment before his climatic speech to the daughter. The father speaks more here than he does anywhere else in the film and I'm sure they didn't just happen to have Nietzsche laying around the prop department and decide to use it because it was just there...
So, I couldn't help but wonder if he wasn't trying to give the dialectical tensions between the old man (society) and the daughter (becoming ubermensch). While there are obvious differences, in the way Nietzsche portrays Zarathustra's transformation and final realization, among other things, there is close enough resemblance to say that this was the directors artistic take on Zarathustra. Although, perhaps the book was merely thrown in there because it was a popular piece during that period (shortly after the war, when the movie's timeline is set), as Nietzsche's philosophy had much influence in Germany, who had a strong alliance with Japan.
P.S. I am not a fan of Nietzsche's philosophy. He clearly contradicted himself and couldn't be consistent with his own worldview and you can see these contradictions within the aformentioned book. In my opinion he is the Ayn Rand of the 19th century, loved only by pop-philosophers and gothic high school kids who have never even read a book of his.