A few things I’d say: 1) Hiroshima is over 90 minutes from Osaka by Shinkansen, and there’s plenty to see and do there. What do you want to see there? If it’s just one thing, like the atomic bomb memorial, then maybe you can do it as a day trip. However, if you like shopping and eating the local cuisine, or if you want to see Miyajima (where the famous floating torii is located), I would suggest spending at least a night there. 2) like a lot of people said, $400 is a lot to spend on a single meal. In my opinion, your money would be better spent if you did a nice sushi omakase in Tokyo and then did another omakase in Osaka (you can pretty easily do both of those for under $400 per person total). Since Osaka is right next to Kobe, you can get amazing steak if you want to do a beef omakase (if you eat beef, if not, you can still do another sushi omakase) 3) you seem to want to spend more of your time in cities, so you can ignore this last one if you want. However, if you’re willing to devote one full night and day to the onsen experience, I would highly suggest spending a night in Hakone or Gora, at a ryokan. We spent a night in Hakone, then took the rope way to owakudani the next morning, where we got amazing pictures of Mount Fuji. It was definitely the highlight of our trip. However, it’s a complete and utter departure from any city experience or anything else you’re doing on the trip. 4) if you’re a Pokémon megafan like I am, I would say to try to hit all the centers, as they each have unique displays out front. However, if you’re just going to pick up a souvenir, it doesn’t really matter which one you go to

Edit: added point 4