if you are in japan you may want to visit akihabara and harajuku.
Akihabara is the place with L-O-T-S of manga and anime stuff. You sure wanna sheck out a maid cafe. ( try @home cafe in akihabara )
harajuku is the pashion part.
Im norwegian so my english is not so well.
hope this help =)
For one thing, you ought to know japanese. After you've got down, you might as well visit some of the famous attractions. Personally, I suggest going to the hot springs. I find them very relaxing.
Be friendly with others. Never eat while walking around the city, it's rude there. You must try the sushi there. I can't tell u much but have a good time!