Is my Itinerary realistic?

Any reason why you can't use the JR Pass for Kamakura and Enoshima?

Cluster your out of Tokyo days together?

If you can't find things to do why do you still insists on staying in Tokyo? Some particular reason you care to share ?

I do indeed plan to activate my rail pass for the day trips to Kamakura and Enoshima. I have some extra days in Tokyo because I like urban settings, know there is a ton of stuff to do, but haven't done all my research yet on things to do in the city. Since I'm staying in Shibuya, I'll be near many concert venues and may end up spending chunks of my evening times there. I plan to check out places like Odaiba and possibly Kawasaki City.

It sounds like even with the more bunched up travel days in the back half of my itinerary, it isn't going to be so hard that I won't enjoy my time in Hiroshima and Okayama. I still haven't decided if it is worth going to Kyoto for such a short time, especially with some of the time I'd spend there being eaten up by travel. I'd love to see Arashiyama, and attend the Ultra Tower concert that evening.

I've finalized my Itinerary, I hope it is ultimately not too straining.

9/4 Arrive at NRT at 14:20, check-in at my AirBnB in Shibuya and explore the immediate area/get my bearings, Meiji Jingu (optional)
9/5 Akihibahara, Ginza, Skytree/Aquarium, Shin Okubo
9/6 Possible cars and coffee meet in Daikanyama (early), Harajuku, Omotesando, Nakano Broadway, Shinjuku Gyoen/Yoyogi park, Omoide Yokocho
9/7 day trip to Yokohama
9/8 Activate JR Pass, visit Kamakura and Enoshima (day trip)
9/9 Odaiba, Tokyo Goverment Building
9/10 Early train to Hiroshima, check-in with AirBnB, Explore the peace park, Carp baseball game at 1830
9/11 Mazda Museum tour 1030, day trip to Miyajima afterwards
9/12 finish any Hiroshima loose ends if necessary, train to Okayama before noon, check-in hotel, Okayama koraku-en, Sambomaster concert 1830
9/13 Early train to Kyoto, check-in hotel, Nishiki Market, Ultra Tower concert 1800
9/14 late morning train to NRT, fly home 1830

Any final suggestions? Things I'm missing out on that I shouldn't/things I have down that I don't need? I'd like to see Arashiyama, but don't want to rush it and expect to spend more time in that area next time I'm in Japan. This trip is all solo traveling, so I can move at my own pace.