If you've forgotten your password for Zaiko or AKB48 Ticket Center, you can reset it.
On the login page, click “Forgot your password?” and you'll receive an email with the subject “Password Reset Request”.
Click the “Set” button in the email and set your new password.
Once you've set your new password, you can log in with it right away.
If you're asked for a password when paying for a ticket, see this article.