It will be just to cover the DO.
Before the DO we're in Ishigaki and Okinawa (no JR lines there ) and as we land in and depart from Fukuoka for the DO, there is a case to be made for either a railpass or for single tickets.

The Setouchi area pass does indeed cover more (both time and area) and is a better value for anyone needing the broader coverage. For me, the main decider is if seats can be reserved for the JR passes online in advance. I do not want to end up in a scenario landing in FUK just to find out that all reseved seat cars between Hakata and Hiroshima are full. (Getting seats on Hello Kitty Shinkansen before they cancel the service on may 17 is also an option and would be a bonus!)

My reading is that single fare tickets with seating can be bought in advance online 1 months prior to departure. So I am basically looking for experiences using the JR West online tool with a JR west pass. If people say they have done it, I am leaning towards a pass. If not, I will probably buy single fare tickets online on march 2.