Yes, a drain.
I had wondered at the time if this was common, and after more travel to Finland and Sweden I discovered that yes, it was common.
The same was true for Italy and most of the continent. They did not bother put drains in the floor.
Here in Japan? They do.
It is a really good idea.
Think about it, bathrooms are wet spaces. They tend to get water on the floor.
Why not make it easy to clean up?
Now what I wonder is if they also put a liner in the floor, or if they are just assuming that this is for "accidents" and have not really water proofed the floor well. That would make sense, because the cost of putting a liner in the floor would be prohibitive (hell though... it is not like any of the countries do anything on the cheap).
I still have a second floor bathroom to do in my house :)