So I guess a browser game is not actually a game you play in your browser, then?
This game can be played in your PC browser and it is possible to filter and block IP connections. This is done all the time. You can circumvent this using a VPN proxy.
This game can also potentially be restricted to certain brands of phones that can only be found in a specific region. This has also been done. You can circumvent this, see Jana's post.
Unless this game is for regular PC browsers too? I can't read Japanese but the site looks like a phone game/app store.
There's connectivity between the PC and smartphones and tablets.
Social mobile games are a wildfire here in Asia. Not just in Japan, but also in China and even in Southeast Asia. It appears to be mostly an Eastern thing. This is most likely because a lot of the popular social mobile games produced here are either anime-styled CCGs, anime-styled pseudo-MMO(RPG)s, or spinoffs of existing popular franchises (recent spinoffs of SAO and im@s come to mind).