The chief innovation here by Atelier Tekuto (a/k/a Yasuhiro Yamashita Architecture Studio) was to build the entire two-storey house out of steel boxes that are stagger-stacked, and each blank space between boxes is occupied by a window. Because the boxes are open-ended--think of the milk-crate dorm partitions you built in college--the interior of each exterior wall becomes a series of cubby-holes, providing a massive amount of storage and obviating the need for cabinets, closets and certain types of furniture.
Interestingly enough, while it sounds like a construction technique like this could be simply erected on-site Lego-style, Yamashita decided (for the sake of precision) to make them off-site in pre-fab, truck-sized units and then haul them to the site:
In order to pile up the boxes, detailed planning took place over the design, structure, and construction. At the same time, from the very beginning, cost and precision of building frame were crucial topics in the process. At first, we planned to assemble each boxes on site but the precision of construction, cost and time became problematic. And eventually, we decided to unitize boxes and fuse them with high-tension bolts previously at factory. The size of unit is decided to respond to the size of truck.
While this is the first we'd heard of the Cell Brick house, it was actually erected in 2004. You can read more about it here.