Itinerary

Hi! Im planning to go to Japan next year and my itinerary now is something like this:
Any HELP? OR SUGGESTIONS?

Day 1: Nagasaki
Day 2: Miyajima
Day 3: Hiroshima
Day 4: Osaka
Day 5: Osaka Himeji Universal
Day 6: Mount Koya
Day 7: Kyoto
Day 8: Kyoto
Day 9: Kyoto Nara
Day 10: Kyoto
Day 11: Ise
Day 12: Kanazawa
Day 13: Takayama
Day 14: Nagoya
Day 15: Nagoya
Day 16: Mount Fuji https://www.japan-guide.com/e/e2172.html
Day 17: Tokyo Western Tokyo Full Day
Day 18: Tokyo Half day trips
Day 19: Tokyo Nikko
Day 20: Tokyo Asakusa and Odaiba Full Day
Day 21: Tokyo

Too many places, a day here a day there.

Just a couple of observations

Day 1: Nagasaki
Day 2: Miyajima That is a big travel day. Are you flying?
Day 3: Hiroshima
Day 4: Osaka
Day 5: Osaka Himeji Universal
Day 6: Mount Koya
Day 7: Kyoto
Day 8: Kyoto
Day 9: Kyoto Nara - Nara overnight is much nicer than a day trip, if you can. I would spend the next night at Nara instead and go from there to Ise
Day 10: Kyoto
Day 11: Ise
Day 12: Kanazawa Is that going to be a big travel day?
Day 13: Takayama
Day 14: Nagoya
Day 15: Nagoya I day in Nagoya is plenty IMO
Day 16: Mount Fuji https://www.japan-guide.com/e/e2172.html
Day 17: Tokyo Western Tokyo Full Day
Day 18: Tokyo Half day trips - Kamakura and Enoshima? Nice....
Day 19: Tokyo Nikko
Day 20: Tokyo Asakusa and Odaiba Full Day
Day 21: Tokyo

Agree with PPs that your itinerary is on the busy / too busy side.

Just one addition, on the day you have Osaka, Himeji and Universal, do you mean you want to go to the castle in Himeji AND universal park? I don�ft think that is reasonable nor achievable.

You could combine Himeji with and evening visit to Kobe though.

Enjoy planning your trip to Japan!

Technically, depending on time of year, it might be achievable and you could go to Himeji and USJ, as long as all you wanted to do in USJ is wander around a theme park and maybe see the nighttime show. You could also make it work if you paid for one of the 4-7 ride express passes, since that would let you skip the long lines and actually go on something, but I am not sure how it works if you need a timed ticket for any of the parts of the park. I've never gone when that has been an issue. This can be a large additional expense though. I've seen those express passes go for more than park tickets. Though honestly, I am not sure why you wouldn't hit up Himeji on your way between Hiroshima and Osaka unless you are traveling during a time period when you expect all tickets to Himeji to be gone.

Ise to Kanazawa is crazy long. It makes more sense to do: Ise to Nagoya (do your sightseeing there) Nagoya to Takayama (visit Takayama and sightsee there) Takayama to Kanzawa (via bus or train if you time for the Hida) and sightsee in Kanazawa and then go Kanazawa to Tokyo. Then visit Kawagushiko as a day trip from Tokyo. You can get there in about 2 hours by direct bus from Shinjuku Station (buses once an hour) vs from Nagoya it's going to run you over 2 hours easily since you need to go by shinkansen to Mishima first and then transfer to a bus to Kawaguchiko.