The “kotatsu” is a truly Japanese invention. Basically it’s a table that has a bunch of thick blankets on top, and then a wooden table top on top of that.
Underneath the table is an electric heater.
So you put your legs under the blanket, and you’re kept warm by the heater. The only problem is some of them have short legs on the table. If you have big legs then watch out, the heater is super hot and you’re likely to get burned!