Okay, so I wrote this a couple of days ago, but recently I got an update I'd like to share.
The user who plagiarized my art updated their post. They credited me for the design and apologized for causing trouble. We're communicating in DMs right now, and it looks like we'll both be on good terms. It makes me happy to know that we can forgive each other, and hopefully, this will never happen again.
I'm keeping the posts up, but I updated everything to show that the user gave credit and apologized along with my response. I feel like there's no need for the DMCA complaint to go through anymore, so I'm working to have it canceled. I hope the user keeps to their word and improves. I worry that if they keep this up, they will meet someone who will take things too far and make the situation worse. The user has incredible art, and I see no need for them to plagiarize other people or not give credit where it's due. I don't want to see them harassed over this.