User blog comment:B214/Volume 21 info & spoilers/@comment-26285797-20160218050953/@comment-1359322-20160218153334

Well Ishibumi might be purposely holding back a few thing since he expressed interest to dwell on the sides of DxD-verse that isn't shown on DxD. A simpler way of saying is he's keeping some things hidden for a potential spin-off like Slash/Dog.