Very good choice my man. Don't puss out and take the cable car up the mountain.
Hiroshima obviously has the Atomic Dome museum which you should go to but another museum which I thought was amazing was the Hiroshima Museum of Art. Not sure if that's your thing but I loved it.
Finally, the boys and girls who worked at Guesthouse Roku were lovely and treated me very well. Obviously you should go eat Okonomiyaki as well.
I am there for 24 hours so first day i am going to Miyajima, then back to Hiroshima for the Okonomiyaki and next morning for the museums and Dome. Not sure about the cable car yet, will see if I have time. I have a long train ride to Osaka which I have only another 24 hours to eat everything lol, then 3 days in Kyoto (with a trip to Nara on the cards I think).
I feel like 7 days in Tokyo may be a bit too much in comparison, I might do a day trip somewhere too, if I get a 14 day JR Pass.