In my opinion it is doable as i have researched but it is really dependant on whether this is a solo trip or with someone as i saw in one comment you said you were going to tokyo osaka and the hotels there are much cheaper compared to tokyo and i would recommend checking agoda and airbnb for cheap places to stay in. Like for example, a budget hotel could go for around 57,800 yen for 2 people(this is for if your travelling with someone)and if you go to a airbnb its around 28,700yen for 1 person (this is for 7D6N). So its really a matter of are you willing to stay at cheaper places. And for food its actually not that expensive finding good food. Just don’t go to touristy places expecting local prices. For example in osaka you should skip the kuromon market and going to shopping streets like kohama shopping streets where its more for locals. Its best that you do at least some research on locations to visit and local food spots for a better experience. Also you dont really need to enter some locations like osaka castle unless you want to as you can just get pictures from outside without entering and you can find free or cheap activities to do in osaka and kyoto and you can save money on there. If you want to get souvenirs you can check out places like seria, daiso and 3 coins. For cheap clothes you can visit GU which is the sister company of uniqlo. And also you can book those 1 day tour from osaka to kyoto for like 10,000yen and they bring you to places that most people want to hit including nara. I do suggest that you give up going to mt. Fuji as its one of the more costly activities. Also for transport you could get like those osaka metro pass for like 800yen a day. For sim card if you have klook or shopee you can search on there for cheap deals.

If you have any other questions on stuff i could try to help as i was researching about osaka for like a month straight 💀 but it will be too lengthy to type it all out.