5 Days allocated to Fukuoka and Hiroshima in October, (best itinerary/use of that time?)

So far I have 5 days allotted to Fukuoka and Hiroshima within a 15 day trip in October. I can pull one day back from the rest of the itinerary if it would be needed.

This is out 2nd trip and the rest of the time is in Tokyo and Osaka and day trips from those areas.

Looking for suggestions on how to use this time.