Most existing bathrooms in the homes of Japan have small size, well that just serves as a room for bathing alone or just soak it. where there is only a bathtub, shower, place to hang towels, glass, and small shelves to put soap, shampoo and other toiletries.
This bathroom is designed specifically for solely for the shower alone, can not be used for defecation / toilet. because the houses usually are there separate toilet and bathroom. with small size bathroom is easy to make, and it takes a lot more room and can you fit it yourself with your home state.