japan in january - one frozen aussie

i’m going to japan in jan/feb for some sightseeing/backpacking and skiiing.
only one problem the last time i went to the snow i could ski through my dad’s legs, so i didnt really care how i looked (although that fluro pink ski jacket was pretty chic in the 80s) + the coldest it gets during winter where i live is like 10C so i dont think any of my jackets would be warm enough.
i need advice on how to rock the freezing temperatures?