This is not really an itinerary — unless you have a couple of months and unlimited funds at your disposal — but rather a listing of interesting places scattered around Japan. Find the region you'll be visiting below, and see if you can work in a few of these into your own itinerary. From north to south:
Onomichi — pleasant little temple town home to many Japanese authors
Tsuyama — a beautiful historic town offering Kakuzan Park, one of the best places in the Chugoku Region to view cherry blossoms in the spring, Shurakuen Garden, and Joto Street, a well-preserved historic road located along the pilgrimage route to Izumo Shrine.
Daisen — a city most famous for Mount Daisen, a great place in the West to hike, climb, and skii (in the wintertime). A walk through the trails to Daisen-ji Temple is quite peaceful and serene.