Visit a Uniqlo as soon as you land. Their "HeatTech" base layers are the unofficial uniform of a Japanese winter.
: The month of major winter festivals, most notably the Sapporo Snow Festival, where massive ice sculptures line the streets. winter japan months
Similar to January, but with a hint of transition. It remains the best month for "monster" ice trees in Zao or seeing the snow monkeys in Jigokudani bathing in hot springs. Visit a Uniqlo as soon as you land
February is when the winter aesthetic truly peaks. While the cold lingers, the days start getting a tiny bit longer. most notably the Sapporo Snow Festival