So, similarly how FILSAMECH was showing up in people's WaraWara Plaza before E3, Sakurai just showed up in mine
If you've got a 3DS, Sakurai will visit you in the Mii Plaza via SpotPass
If you go to notifications before clicking on this Mii, he'll disappear. If that happens, create a quick new account, and you'll see him there along with FILSAMECH probably. Remember to click "Save This Mii".
If you've got a 3DS, Sakurai will visit you in the Mii Plaza via SpotPass