Spontaneously booked a two week trip to Japan in August. We're landing in/flying out of Osaka but willing to move around. Any advice/must-sees/must-tries? Neither my husband or I have been so we're open to anything!

Dotonbori is a good spot in Osaka. Lots of good places to eat

Make sure to check out Dotonbori, Osaka Aquarium, Uncle Rikuros cheesecake, Ichiran Ramen, Kyoto and Nara are close by Osaka so definitely take a train there.

Hiroshima Peace Memorial, Kyoto inc. Fushimi Inari Taisha and Arashiyama. If you have a chance stay at an onsen. There’s a LOT to see in Japan, depends how far you venture.

Book accommodation ASAP as lots of festivals are happening in August and some towns may not have anywhere to stay.

Peach Airlines flies out of KIX so lots of cheap flights. You can get the discounted train pass to Osaka/Kyoto. Details here: https://www.westjr.co.jp/global/en/ticket/icoca-haruka/
WESTJR.CO.JP
ICOCA and HARUKA

Also, get a portable WiFi, way easier to connect and cheaper too.

Look into the Japan rail pass for transportation.

I've got some leftover yen from my trip earlier this year. PM me if you want to buy it!

It will be HOT. We were there in August two years ago and Osaka was about 35 degrees, plus the humidity.
There is a big festival in Kyoto the middle of August where there are symbols lit up in fire on the mountains.

I have the most recent version of the lonely planet guide to Japan. It's in very good condition. We used it to find things that interested us specifically. There are plenty of maps and tips. Are you interested in buying it?

you can do a day trip to Kobe for Kobe beef!

If you have 2 weeks you need to decide how much long distance travelling you want to do.
Nara is an easy day trip from there and worth the visit.
Kyoto is a must. You can stay in Osaka if you like as the shinkansen gets you there in like 15 minutes but you will want at least 2 or 3 days to explore Kyoto. I just recently stayed at a gorgeous hotel with a public bath I can recommend. Look into visiting Koya-san for a mountain Buddhist experience.
If you are up for moving around or longer trips, Tokyo is for sure a 4 or 5 day adventure and takes 3ish hours by train so plan to stay there if you go. Hiroshima (for me) was all about the peavlce memorial and can be seen in a day. A trip to Miyajima is worth it too.
Jr pass is only worth it if doing lots of travelling. We did 2 weeks but got the 7 day pass so we activated the day we left Tokyo and it ended the day we returned. To help calculate if it is worth it, visit hyperdia.com as you can enter your to and from stations and it will show you the exact path and cost. I also used it when there to figure out getting around.
If you are a Disney nut and doing Tokyo, Disney Sea is worth a day. Osaka has universal Japan but I have never done it.

Pm me if you need any advice or help!

Portable wifi is a must- stay in Kyoto, if you wanna do more traditional things than city things, if you get a JR pass, check out Tokyo and Hiroshima

Do an “Onsen” it’s a hot springs/spa. Also too, be aware that many of the public bathrooms don’t have toilet paper. Many people stand on street corners and hand out little packs of Kleenex with advertising on it...TAKE IT!

I have spent lots of time in japan, all over the country, and the bathrooms all had toilet paper. What they didn't aleays have was soap to wash hands at the sinks. So a tiny hand sanitizer and a hand cloth to dry with in a purse or bag is a good idea.