You can find plenty of things about the (raw) denim subculture as far as Japan goes, this is probably a decent intro article: https://www.heddels.com/2013/06/what-makes-japanese-denim-so...
Note that none of these brands are really literal workwear. They're not competing at all with carhartt (Most of these pairs will run you $300 at least eg.), and almost everybody who buys a pair is going to buy them for the experience/authenticity and aesthetic (Americana)
Uniqlo sells a variety of jeans. While cheap and good for the price, it isn't exactly high quality.
Is carhart really work wear? All the cool kids wore carhart in junior high 15 years ago where I lived.
Yes. It made the to 'cool' on the back of the rugged reputation, but Carhartt jackets are still a common sight on construction sites, out hunting, and so on. The jackets at least really are that good - waterproof and extremely sturdy.
It's sort of the same role Red Wing boots have slipped into - they count as cool now, but they're still totally viable as heavy workwear.