3 days: Fukushima<->Tokyo<->Osaka

Hi everyone!

I'm currently planning my last two weeks of my 5-week travel in Japan. I've started in Osaka, went to Hiroshima for a few days, Tokyo for a few, Roadtrip around Izu, Hakone onsen, a few days in Nagano, and now upcoming two days in Nikko and a few days in the Fukushima prefecture. I'm planning a few more days in Tokyo and Osaka on my return (flying out of Osaka), but I still have 3 or 4 days left to spare which I haven't decided on a location to spend them on.

Now I know this is a wild ask, but what would your recommendations be? Spend a day longer each in Fukushima, Tokyo, Osaka? Or rather visit a new city or two in between Fukushima<->Tokyo or Tokyo<->Osaka? Would love to hear your opinions on what I definitely shouldn't miss, thank you so much!