Japan is a place I could go back to over and over again, in all seasons. But I do like Winter the best because you get to enjoy snow and related activities be it skiing or snowboarding while enjoying the mountains at its best. After all, Japan's snow powder quality is reputed to be amongst the world's best. Do consider the 3-layer rule to stay warm and toasty while enjoying winter sports - the base layer to wick moisture away, a mid layer to trap heat, and a waterproof outer layer for protection against weather elements. For the base layer, I'd go with either SmartWool or Icebreaker, both of which are great brands to get a 100% merino wool layer for a breathable and non-itch texture. I'd recommend a mid-weight 200g for a comfortable experience while skiing; light-weight is best suited for warmer weather, whereas heavy-weight is great for standstill activities such as photography in winter weather. Fleece jackets are common mid layers, and my current Marmot jacket serves me well in keeping the heat in. A good outer ski jacket should be waterproof, and Gore-tex is great at this; underarm ventilation zips are a great help especially when you are skiing hard, out on a bright sunny day and overheating. Finally, a lift pass pocket is essential so that you wouldn't have to worry about taking it out from your lower pockets repeatedly. Have a blast on the slopes!
