Given that Zeref used the dead body of Natsu to create END, now that we know that the Zeira in the recent Fairy Tail Zero chapters isn’t real (an allusion of Mavis’ creating), that she died on Tenrou Island, it is safe to say that Zeref used Zeira’s body to create Sayla.
I mean, they look very similar, they are both associated with books, and their names are spelled almost exactly the same in Japanese, the difference being a tenten: セイラ (Seira) vs. ゼイラ (Zeira).
I mean, their faces, especially the eyes and hair, are the same
Because of this, I have reason to believe that Zeira was used as practice for reviving Natsu. Clearly, Sayla did not have any memories of her past, meaning that Natsu, when he was revived, may not have had any memories of Zeref.
Carole Ann Ford has said that Peter Capaldi would be very interested to see her reprise her role as Susan Foreman.
Speaking in Doctor Who Magazine issue 487, Ford - who played the granddaughter and companion of the First Doctor - states that she is also up for reprising the role: “Of course! Are you kidding?”
She then explains how the conversation began: “They invited us to the studios in Cardiff [during ‘Last Christmas’ filming]. It was great. It was lovely to meet Peter [Capaldi]. A lovely man.
“…[Peter] started saying, ‘Oh, you should come back!’ I said, ‘Yeah, I’d love to come back!’ He was running around the TARDIS saying, ‘She’s got to come back! She’s got to come back!’”
Ford went on to share her opinion on Capaldi as the Doctor: “I had seen some of the performances he’d done as Doctor Who and I didn’t like the way they wrote him at the beginning. I thought, ‘What’s going on here? Give him a chance!’ They portrayed him as someone who was so prickly.”