Ao3 removed the fic and sent me the following message:
After investigating your complaint, the AO3 Policy & Abuse committee has determined that the work “The Boy Who Has Fire” by Familiar_Anonymous did in fact contain material plagiarized from your work “Birth of the Serpent King”. This is a violation of our Terms of Service, section IV.E., and accordingly, the offending material has been removed. However, we have also determined that there was insufficient evidence of plagiarism of the other works included in your complaint.
I checked the link and the story is no longer on a03. I'm relieved but also still irritated by the plagiarism and the four month wait on a response.