If you can't reset your login/password to the e-mail address you recall that you registered with pixiv, it may be that in fact, you registered with a different e-mail address.
The password reset form will only send instructions to your registered e-mail address. Please try logging in to the e-mail address where you receive update notifications or notifications of support, or try resetting your password for this e-mail address.
■ Password reset form
https://accounts.pixiv.net/password/reset
If you made a pixiv account using an Apple ID
Please refer to the FAQ below.
I made an account using my Apple ID, but I can't reset my login/password
If you can receive e-mails at your registered e-mail address
After confirming your account based on your payment information, we will direct you on how to change your e-mail address. Please refer to the following in order to continue.
■ Credit card payments
If you want to inquire using your credit card number, a dedicated form for your credit card information will be issued.
Please include the following information in your inquiry.
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I want an account verification form
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■ PayPal payments
Please inform us of the transaction ID you got in the e-mail from PayPal as you were charged.
■ Convenience store payments
Please let us know the creator you supported, the receipt or confirmation number, and the date and time of the payment, as written in the confirmation e-mail you received at the time of payment.
■ pixivcoban payments
Please send us the transaction date and time, transaction ID, and name of the creators you supported listed in the e-mail you received when using pixivcoban.
Inquiries
https://www.pixiv.net/support.php?mode=inquiry&type=17&service=fanbox