The residential home is located in Osaka and was constructed on what is known as a flagpole site* (旗竿敷地).
The home sits, like many homes in Japan, in a highly dense residential neighborhood. Working under these circumstances, the architects conceived the slope as having 2 purposes. First, it would create an ambiguous, undefined space that would be used not only as a means of transportation, but also as a gallery space, a child’s play area, or simply a place to sit down.
Second, by wrapping the slope around the sides of the house, the resident will visually and consciously obtain a sprawling sense of space as they move from one room to the other.
*Flagpole site: a piece of land that is shaped like a flagpole (a), characterized by a narrow path leading to the main site, which is set back from the street. The flagpole site is a real-estate phenomenon that, is indigenous to Japan. It really began to spread after the end of WWII and can be attributed to homeowner psychology at the time. To own a home was to contribute to the rebuilding of Japan as a nation. It was considered one of the most patriotic things you could do.
Additionally, if you were going to own a home, the ideal shape was that of a samurai residence (武家屋敷), which happens to be defined by a perfectly square-shaped home that sits perfectly in the center of a larger square-shaped yard. However, in dense cities where land comes at a premium, the yard was forfeited. The only prerequisite for building a home was that it be square-shaped (size was a non-issue) as the perception that square = value quickly become embedded in the mindset.
To this day the product lineup of most homebuilding companies in Japan are based on the old samurai residence. This has resulted in neighborhoods being hashed up into small square-shaped land sites with a foot or so of dead space between neighboring houses. This is also the reason why trees are scarce in residential neighborhoods in Japan – squares don’t accommodate any sort of yard. [source]