If you created a pixiv account using an Apple Account (Apple ID), follow these steps to log in.
■ How to log in
Go to the pixiv login page. Click "Log in" and select the Apple logo under "Log in with an existing account". Enter your Apple Account login details.
If you can't remember your Apple Account password, reset it using the following link.
■ Reset your Apple Account password
https://iforgot.apple.com/password/verify/appleid
If you can't log in with your Apple account...
First, please try logging in with the e-mail address where you receive notifications about your support and updates.
If you can't log in with any e-mail address you recognize, check the e-mail address ending in “@privaterelay.appleid.com” registered to your pixiv account, and then try “Log in with e-mail.”
You can check the “@privaterelay.appleid.com” e-mail address registered to your pixiv account by following the steps below.
■ How to check your e-mail address
1. On an Apple device such as an iPhone, open “Settings” > “Apple Account (your name)” > “Sign in with Apple” > “pixiv.”
2. On the pixiv login screen, select “Log in with e-mail” and use the e-mail address ending in “@privaterelay.appleid.com” displayed under “pixiv.”
▼ pixiv login page
https://accounts.pixiv.net/login
If you created a pixiv account using an Apple Account (Apple ID), your registered e-mail address might not be the one linked to your Apple Account.
If you enabled "Hide my e-mail" when signing up with Apple, Apple automatically generated a random "@privaterelay.appleid.com" address for your pixiv account.
Any e-mails sent to this address are automatically forwarded to the e-mail address linked to your Apple Account.
To learn more about privacy settings, please check Apple's Help pages.
https://support.apple.com/105078