1. What is your budget
2. Which cities will you be staying in?
3. What do you want to see?

OK - you don't seem to have much idea of what you want to do yet, so I'll just make one suggestion - take a look at this website:

Tokyo travel guide for essential sights & attractions in Tokyo Japan - UnmissableTOKYO.com

I've done most of the things it suggests and I can guarantee that they are all really great unique-to-Japan experiences.

Other than Tokyo, be sure to go to a hot spring resort at some time (Hakone is great, and very day-tripable from Tokyo). And Sumo will be on in January in Tokyo - be sure not to miss it.

It really depends on your interests, what you like, what you want to see and learn, etc.

I was in Tokyo for 2 weeks and I felt I didn't have enough time to visit everything I wanted to see, so make sure you plan ahead, maybe leave yourselves a day or two of free in case you might find out more of what you want to do when you get there.

Also, I found that making friends with one or two people online before going helped me a lot. I was glad to have them to hang out with and visit Tokyo with when I went, especially since one of them was good in japanese, since I'm not. Lol

Traveling Smart in Japan
 

Hey there,

There's a lot of planning involved if you are traveling for 1-2 months. Plenty to see, do, eat, drink and more.

If going for over a month, I suggest at least 3 weeks in Tokyo and its surrounding cities, another week in Kyoto/Osaka/Nara/Kobe area, and another week in Hiroshima and perhaps further south.

January is of course winter time, so going south (perhaps even Okinawa) could be nice, especially if you are into outdoor adventures which would be difficult in the cold.

I have a lot of things on my blog that could be useful (http://smartjapantravel.wordpress.com), and I am soon publishing a book that shows the right way to experience Japan and how to do it economically.

Personally I'd get out of Tokyo after a few days, but like the others I'm not sure what you like! Japan has tonnes to see, and all of it very varied. If you like the bright lights and big cities stick to them, but I think Japan is a lot more than that, there are beautiful areas of coastline and countryside which give you a better understanding of the country and its customs.

As you are going for so long, you can definitely travel right from the north (Hokkaido) to the south (Okinawa) and experience lots of things along the way. How are you planning on travelling around, most people buy the Japan Rail Pass but you would need 3 x 21 day ones perhaps, very expensive! If youre budget is not that large then you'll need to look into places you want to stay in for a while, and buy fewer passes, and activate them only when you leave a place heading to the next. Japan Rail Pass - buy the JR Pass online

Three weeks in Tokyo is about two weeks longer than anyone probably needs to see what they want to see.

I have a feeling he meant 1-2 weeks, not months.

For some reason people think the longer you spend in a place on vacation, the better. Two months on vacation in Japan could cost several times that in salary. On top of that, Japan is not a "resort location" so unless you have bottomless bank accounts, spending weeks in any city will frankly get boring and expensive unless you are visiting friends or family.

I'm going to have to disagree - Tokyo and its surrounding areas have more than enough to offer for 3 weeks. The trip is actually cheaper when you move around less.

Unless you have a bottomless money supply, I think spending more than a week in Tokyo is going to leave you scratching your head for what to do.

Things in Tokyo are quick and easy to get to, relatively, so seeing two and three attractions in a day is no problem.

So after Tokyo Tower, Akihabara, Harajuku (Meiji Jingu Shrine), The Tokyo Metro Govt building, Ueno Park, Odaiba, Ginza, Kaminari-mon, Yokohama's China Town, Kamakura for the Daibutsu and maybe a day at Disneyland, and a night at Nikko, how are you going to fill the next two weeks?

I think naive travelers make the mistake thinking more is better. "The longer you spend in a place the better the trip will be. " I know by experience this isn't always true.

I have taken groups of high schoolers to Japan, an invariably they are disappointed we don't schedule a week of traveling in Tokyo. At the end they are always happy we schedule just three or four days.

I took teacher of Buddhism on a tour of Japan, and after 15 temples in a week he finally said "I have seen enough." Even though he originally wanted to see about twice that many.

Sometimes when traveling less is more.

Since it comes to discussing "how many days are adequate for visiting Japan", I'd like to ask my question here.

I haven't been to Japan before, so it will be my first time. I guess 5 days falling on a weekend should be good for me? (for example, Thursday to Monday)

To OP, I think you should think about transportation too. If it's your first time too may be you can visit those popular spots as the others have already mentioned.

That's a long way go to for just five days.