Because Japanese people are expected to dress up but also want to express themselves, we see many different styles in Japan.
I personally really like Japan's fashion tastes as I can test out many outfits. Because guys do not have as much variety of clothing as girls do, it can sometimes become boring to buy clothes. It all looks the same and the only thing that's different is maybe the color, or maybe we'll stumble on a cool jacket. In my opinion, unless we turn to online shopping, buying clothes for guys is kind of boring. Japan expects people to look proper in public, and so created a wide variety of styles, which I personally enjoy as commonly, men often do not have a wide variety of clothes to choose from.
The trends here follow East Asian beauty standards, meaning whatever is popular in South Korea, China, Taiwan, etc. Have you heard of K-pop idols? Could you name a few? Very often, the items and accessories that idols wear sell out within minutes. It's pretty normal for an idol's fashion item to sell out within minutes of their picture being posted online.
Here's an example from Business Insider: Jungkook from BTS was photographed wearing a silver chain necklace. Well, guess what? The online store, The Tuewid, sold out the next day for both its gold and silver versions! An even funnier story was how Jungkook accidentally caused a fabric softener shortage by just mentioning its name. Now imagine certain Japanese idols's accessories selling out as well. All in all, we can see that many people follow idols, who are, for better or for worse, the trendsetters of East Asian beauty standards.
Japan is known to have several more unique fashion styles too. Harajuku is known to be the fashion district of Tokyo.
