I found out one guy "icze4r" at pixiv using Stable Diffusion to steal images from e621 and from different artist to generate "art". e621 should ban the use of the api or the access of e621 to those sites, it is so painful to see the amount of work stolen by this guy. I suggest to every artist to block him at twitter too
https://www.pixiv.net/en/artworks/106394156
Updated by Cinder