The 750k model I saw was steel frame modular home, soon theory you could re-arrange it if you got bored of the layout - though I suspect that comes with a hefty cost.
It’s basically a large lot where all the major home builders set up their model homes and have detailed sales walkthroughs. Home builders in Japan are at an industrial scale with lots of economies of scale and modular parts, yet a surprising amount of customization is possible. Companies like Toyota and Mitsubishi have home divisions.