(Myth/Auth)how to input username in Japanese

Thanks for everything.
I was able to add login functionality to an existing app using Myth/Auth, but the next step is that Japanese cannot be used for user names. Can this be solved by customizing Myth/Auth?

I am now trying the following commands.

PHP Code:

php spark auth:publish
Publish Controller? [y, n]: y
  Created: Controllers/AuthController.php 
Publish Models? [y, n]: y
  Created: Models/LoginModel.php
  Created: Models/UserModel.php 


If I can exclude `alpha_numeric_space`, you can probably input Japanese, but it hasn't worked yet.