The design a Japanese futon is, well, Japanese!
What makes a design Japanese? The item is useful, easy to clean, and maximizes the use of space.
The coverings are washable. The futon itself is taken out on sunny days and hung on a railing to air out. Thy are also beat with a wand to get the dust out. This is the same way western floor rugs were cleaned before vacuums.
A futon maximizes the use of space because when it is not in use, it is rolled/folded up and moved close to a wall, thus freeing the space to serve for more than a bedroom.