A kotatsu is essentially a table with a blanket, and heating underneath. It goes back many years, but charcoal braziers have now been replaced by electric heaters.
While many people did not get familiar with masks until the COVID-19 pandemic broke out, wearing a mask in Japan has been socially accepted as normal for many years.
Toilet slippers are for bathroom use only. These can be found in some households, as well as at some traditional restaurants, ryokan inns, and chaya teahouses.
Japan's love hotels, aka boutique or fashion hotels, are lavishly decorated and intended for those who value privacy and a unique experience. There are usually two rates: "rest" for a romantic escapade during the day, and "stay" for those looking to spend the night.