On February 16th (Monday), we've released a function that will let you connect your pixiv account to Twitter. You can also log into pixiv using Twitter authentication on the browser (http://www.pixiv.net) and smartphone (http://touch.pixiv.net) versions of pixiv.

For users who already have Twitter accounts, this function will allow you to use just one account to use both pixiv and Twitter.
*By connecting your Twitter account, we will not send any tweets, direct messages, follow users, or change your profile.

From the URL below, you can add your Twitter account on pixiv.

Browser version: http://www.pixiv.net/setting_social_login.php

Smartphone version: http://touch.pixiv.net/setting_service.php

Also, new pixiv accounts can be made through Twitter authentication.
If you've got a Twitter account and haven't registered for pixiv yet, consider creating one!
Register a new pixiv account here.