User blog comment:Jopjopjop/Volume 20 Spoilers/@comment-72.89.42.56-20150723155731/@comment-3965848-20150723163735

My guess it's probably the Incinerate Anthem that DxD got a hold of, since it's the only Longinus I know of without a user.

But since they didn't mention the name of the already known SG, it could be either Innovate Clear or Telos Karma.