User blog comment:Omega natsu2/Chapter 388: Erza vs. Minerva, Predictions./@comment-7418318-20140609075616/@comment-5668006-20140612210144

It's definitely either Arba or Sheba. I'm leaning towards Sheba thiugh just because of the character development and devotion to Solomon would make the betrayel that much more of...a betrayel. Also, apparently Sheba is second strongest