Creating an account is a simple and straightforward process.
Go to https://cryptowars.jp and click on the Play Now! button.
Once in the authentication page you're offered two options: Signup or Login and signing up is why you're reading this guide for click on the Signup button to continue.
Enter the requested details (Username, Email Address, Password, and Password Confirmation) and click on Sign Up once done.
An email will then arrive to the inbox of the set email address for confirmation and once you click on the provided link you're good to go.
Other things you can do on this page is login (duh) or recover your password in case you've forgotten it.
If the later happened just click on Forgot Password and follow the instructions provided to get back in the game.