I am there for 14 days. Planning on staying in Tokyo and Kyoto and moving around from there.
I'll let you know where I went and the things I enjoyed the most and least:
Flew into Osaka - stayed there for four nights. Loved it there! If you're into a gritty urban vibe with unbelievable food (the best in Japan imo) you would love Osaka. It just had a different feel to it than everywhere else we went. Would definitely recommend. The aquarium is pretty cool too although not much better than Toronto's. Would recommend regardless.
Trained to Kyoto to stay for five nights. More of a sight seeing place. I liked it, very natury and touristy. My favorite part of Kyoto was the bamboo forest and monkey park on the top of the mountain. Get a nice view and hang out with monkeys at the same time? Was a great day. It was here where I activated my 7 day JR pass (would recommend if the math checks out) and went to Kobe for a reservation that we had for a steak dinner. Reasonably priced for what you get and it was a life changing experience. Restaurant is called La Shomon. Overall Kyoto was alright. People seem to either love it or not he a huge fan. I was temple'd out by like day 2 personally. It was nice and all but out of everywhere it was my least favorite city. Very picturesque though so take lots of pictures. It is beautiful.
Then went to Hiroshima for two nights. First night we visited the Peace Museum and hung out around the streets of Hiroshima. Museum was 10/10 and Hiroshima is a very nice city overall. Next day we went to Miyajima island. 10/10 as well. Climbed mount misen, ate some oysters. Typical day in Japan.
And from there we took the train to hakone to relax a bit at a ryokan. Onsen was nice and refreshing (although not a must-do) and the kaiseki style meal was a once in a lifetime experience. Would go again just for that. It was included in the price for the night.
On that leg I transported my luggage from my Hiroshima hotel to my Tokyo hotel so I did not have to carry them around in hakone. Japan has an unbelievably efficient system for luggage transport - talk to your hotel for that, it's life changing. And cheap!
I then went to Tokyo for 7 nights. Found Shibuya over crowded and overrated. Shinjuku was more my scene; almost Osaka style urban grit and a bitch ass red light district (feels amazingly safe). I recommend Shinjuku Gyoen. Tokyo was mostly wandering through the different districts. Loved it outside of Shibuya. You can take day trips to Kamakura (mini Kyoto so if you're going to Kyoto already I do not recommend) or Mount Takeo to get away from the urban life for a bit. I didn't do either but they were options. Overall Tokyo didn't really have one thing that stood out.. it's the sum of the parts for me. Never a full moment and each district had its own feel and charm. Wander as much as possible there.
My favorites were osaka and Tokyo. I feel like I'd never run out of things to do in either city. Hiroshima for two nights was perfect and hakone was perfect for one night although imo not a must-do. Kyoto for five nights was too long for me personally but there is more than enough to do there for at least 7 days. If you're into sight seeing and visiting various temples I definitely recommend it. Just make a day trip to Osaka and if you want to, making a pitstop for a night in hakone isn't a bad idea before hitting Tokyo.
Last words of advice: bring good comfy walking shoes. There will be walking. And a lot of it.
And pack light. Its not a third world country. You can buy anything there. And you can do laundry there or **** it, handwashyour shit. You don't want to be lugging around heavy shit in Japan.
