The spirit in Cyrus's necklace... WAS HIM THE WHOLE TIME!!!!

Yes that's right, it was Cyrus in Cyrus's necklace all along! Specifically, it was his memories, which had been separated from his personality and put in the necklace (along with the immortal Muse soul). That's why the necklace spirit was always on the same page as Cyrus - they're the same guy! And it makes pages like this very, very ironic.