When we have to talk about fashion and trends in Japan, Harajuku (one of Tokyo's districts) comes up most often. The average age of Harajuku dwellers seems to be a bit younger than in Shibuya, but Harajuku is a great fashion neighborhood in Tokyo.
The main street in Harajuku is called "Takeshita Dori", where everyone can walk between large shopping malls and smaller, intimate and independent trend shops, where you can find fashion clothes for both women and men.
In Harajuku, the Japanese people you'll walk into wear all sorts of trendy or excentric clothes, without wondering whether others like their style or not. Some will even dress as cosplay, especially on week-ends.
Some time ago, Harajuku has seen the opening of both and Evangelion store (a very famous anime from the 90's), and an AKB48 store (the number 1 Japanese-pop seller girls band).
How to get to Harajuku
Harajuku Station is on the JR Yamanote train line that goes around Tokyo
Location reachable with the JRP : order your Japan Rail Pass (from ~US$ 272)
How long / when to visit
Very crowded on weekends