Where it comes from
The technique is Japanese and unusually literal, nuru is simply the word for slippery. It grew up in Kawasaki's bathhouse quarter, where nori-derived gel, prized because it holds heat and refuses to soak into skin, turned washing into an art form with its own apprenticeship. The export version has changed remarkably little: the gel is still seaweed, the method is still full-body, and the only real adaptation Amsterdam made was teaching it to travel, bottled warm, packed with its own sheet, and carried up hotel stairs after dark.