The answer is, all over Japan. The pull down menu on the booking page will show you all the areas Nagomi Visit hosts are available.
The following map which is linked under the pull down menu on the same booking page will help to see the locations visually. Some popular destinations are Tokyo, Kyoto, Osaka, areas close to Hakuba-mura such as Matsumoto and Nagano, Hiroshima, and more. The Nagomi family keeps on growing every day so make sure to keep on checking the list!