Suggestions for extra days we have available

I have been reading many posts and realize I should ask help. I plan to be in Japan for 4 weeks in June. The first week will be in Wakayama, the last week will be spent in Tokyo. In between, we want to visit Hiroshima, Iwakuni, Nagasaki, and Kawaguchiko. I would like to break up the long train trip from Nagasaki back east. Do you have suggestions where we might go using our rail pass and what we might do? I would love to add a side trip. We need to be in Kawaguchiko on the 21st. Thank you.