Anyone with an account at The Sandbox. As long as they have a Windows PC or an Apple Mac that meets the required specs to run the Alpha Client.
If you use a VPN, make sure that it is not set to Japan, before participating in the Alpha. Japan has strict regulations on cryptocurrencies, which will cause issues for you later when you try to claim rewards. There's nothing that The Sandbox will be able to do for you should you be identified as using a Japanese IP address.