I've had a request to explain the kotatsu. Only too willing to oblige.
Here is the wiki on it, which has some helpful photos. Basically, it's a table with a heater underneath, and a skirt (comforter), and you sit under the skirt so it can keep you warm. In a country with very little central heating and next to no insulation at all, localized heat is very important. Without things like a kotatsu, you are in fact attempting to heat the whole prefecture if you essay to keep your entire homespace warm.
Relatedly, I suddenly feel less like people with heated toilet seats are "spoiled" and more like I seethe with envy when I consider their situation.