User blog comment:B214/Volume 22 spoilers/@comment-103.252.227.50-20161108134812/@comment-10330822-20161113142021

Well, its not like she is his permanent Queen, he's just a stand-in for the tournament. I would like it if he was using Tiamat, because she is very strong in her own right. Then maybe after the WRG, she just becomes a familiar, and Issei picks another person for his real Queen.