She really is the real athy. She died in the first timeline and reincarnated in the modern world. Then she overdosed herself and live back again in her first life in the second timeline.
So the black magic Lucas was saying is probably Claude used black magic maybe because there is a possibility he wants to use Necro magic meaning he wants Diana to live again. Or that memory wiping curse he did to himself to Diana is the Black Magic he used to forget about her. I really wish that we get to see a throwback of Claude and Diana maybe that answers our question. I mean there could be a possibility of Lucas using his magic with athy to travel back in time how her parents met she could find her answers there. SINCE spoon changed the story from the novel. And she USE THE NOVEL ONLY as reference to make the comic yeah, there may be a case. Just don't overthink (speaking to myself) I mean that would be cool to use a spell that can go back to the past.
And also cool Claude trying to return Diana back to life after she gave birth to Athy. Or there is a story behind the first timeline why Claude wants athy to be dead because he blamed her that because she was born in this world the love of his life died because of Athy. Then he wasnt able to meet her until she was 10 in the first timeline, then that is when at 14 she debuted and Jeanette came to the picture cause he believed Jeanette was his daughter. Because Claude used black magic to himself for memory wiping Diana in his mind, and Athanacius used magic on Jeanette that is why Jeanette is the only person that can stabilize Claude's headache BUT Jeanette had Black Magic and she does not know about het powers at all. (Talking to myself, my mind.) I hope we get to have answers in the next chapter when Lucas explains it all to Athy.
Cheers!
Also, there could be a possibility of a Time Travel Arc.