Hello,
If you accidentally lost your quick registration email without saving it, then unfortunately your account cannot be retrieved. :( Your email address is the identifier for the account. You can try sending CS a ticket through the in game platform to see if your information can be retrieved via your username, but it is unlikely they will give this information out (since that is personal information). Here is the link to try.

https://support-center.oasgames.com/

However, if your issue is that you've misplaced which server you are on (possible, since you are actively on an account right now, you c*ways check the list in Recharge Center:

https://pay.oasgames.com/oasispay/web/index.html?gid=narutoen&lang=en&server_sid=&uid=?

as it will show all the created characters and what server they are in on that account.