So how did the Japanese become so clean-conscious?

It certainly isn’t a new thing, as mariner Will Adams found when he anchored here in 1600, thus becoming the first Englishman to set foot in Japan.
 In his biography of Adams, Samurai William, Giles Milton notes ‘the nobility were scrupulously clean’, enjoying ‘pristine sewers and latrines’ and steam baths of scented wood at a time when the streets of England ‘often overflowed with excrement’.
The Japanese ‘were appalled’ by the Europeans’ disregard for personal cleanliness.
 In part, this preoccupation is born of practical concerns. In a hot, humid environment like Japan’s, food goes off quickly. Bacteria flourish. Bug life abounds. So good hygiene means good health.
But it goes deeper than that.
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