Dude, check out youtube as some guy has backpacked the length of Japan. If you are seriously going to get to JP without flying then good luck!
No seriously, Take a friend and video the whole trip, edit it and then try to sell the video to an agency. You will not do it the way you are saying unless you are already 1000 miles into the trip and get media interest and thus sponsorship offers. you must also have a good reason for your voyage and not just CUS I WANTED TOO!
There needs to be some thread of interest that captivates people. Again take a look at the youtube video of the dude who walked the length of JP.
Kintaro Walks Japan