Your pixiv ID is the login ID that you enter when you log in to pixiv. You can also use your e-mail address for this purpose instead of a pixiv ID. However, this will not turn your e-mail address into a pixiv ID. Your pixiv ID is important registration information. Be sure not to forget it and to keep it safe.
Your pixiv ID can be changed once per account.
Once you change it, you cannot revert to the previous pixiv ID.
In the pixiv ID field, enter the string of text that you would like to use, composed of alphanumeric characters, hyphens ( – ), and underscores ( _ ). You cannot register IDs identical to those that are already registered on pixiv. If you receive an error message that says that the ID is already in use, enter a different string of text and try again.