The Japanese Home
The Bathroom isn't the Toilet
Whereas in the west we tend to place all "bathroom related" utilities within one room, the Japanese make a clear distinction between the actual place where you bathe and the toilet by always placing them in separate rooms. The area that holds the shower and bath will also contain the sink where you brush your teeth, wash your hands, comb your hair and so forth.
In most homes there will be only one bath sink location and it will likely also hold the home's only large mirror. This can get a bit hectic in the morning when everyone in the family is waking up and needing to tend to their respective morning rituals. As far as toilets are concerned, the homes with one or two toilets are split at around 50/50. However, if a home has two toilets, it will still usually only have one bath sink and large mirror, even if the home is relatively large.