Tokyo is known for its out-of-this-world street fashion. Harajuku is the place where you can surely find the most different styles and the weirdest outfits.
There are shops with all kinds of clothes you can imagine. Most popular is kawaii stuff meaning all kinds of cute clothing, food, toys and accessories. Other stores go to the opposite extreme selling gothic, grunge and punk items.The best thing about this place is that it is socially acceptable to have a completely crazy style. The more accessories the better. When visiting Tokyo you should definitely go to Harajuku and see this insane fashion show.
For a more detailed guide to the particular styles from Tokyo streets, see here. For news on trends, street fashion pictures and shop openings, visit this website.