Hi, This should have something to do with Microsoft's strategy of whether or not you can apply for a trial version. For some countries, such as Japan, customers cannot request a trial environment on their own, they have to go through Partner.
Use email account in JP.
So, If you really need it, you can create a new Azure Active Directory in Azure Portal, choose US in Location. And then use the new user inside the domain to apply.
Hope this will help.
ZHU
