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^This, the temperature specific waxes are colour coded (temperature in deg. celsius):
=> Green -10 to -32
=> Blue -5 to -12
=> Purple 0 to -8
=> Red 3 to -4
=> Yellow 10 to 0
Japan doesn't get super cold very often, also remember you're looking at the snow temperature rather than the air temp. so a -5 to -12 wax is probably about where you want to be.
Japanese pow tends to be very very low water content which makes it very sticky. You'll want to be getting a wax probably once a week at the very least or you'll be grovelling on the traverses/cat tracks and hating it.