Call it an antidote to fast fashion: Japanese jeans hand-dyed with natural indigo and weaved on a clackety vintage loom, then sold at a premium to global denim connoisseurs.

Unlike their mass-produced cousins, the tough garments crafted at the small Momotaro Jeans factory in southwest Japan are designed to be worn for decades and come with a lifetime repair warranty.

On site, Yoshiharu Okamoto gently dips cotton strings into a tub of deep blue liquid, which stains his hands and nails as he repeats the process. The cotton is imported from Zimbabwe, but the natural indigo they use is harvested in Japan — its color far richer than synthetic imitations, according to Okamoto.