The topic of how religion affects entertainment would, by itself, be enough to fill 20-25 minutes. And you wouldn't need to go into any discussion about food or martial arts. Think about how religion affects the west's view of entertainment, and then think about how the difference in attitudes toward religion and morality affect how Japan views entertainment. So religion > manga > anime > games could be an interesting subject.
Or the written language alone is a huge topic that would provide at least 25 minutes of information.
If you just throw in a bunch of themes: writing, food, language, art....etc... your discussion lacks coherence, and you just end up listing a bunch of cliched stereotypes.