User blog comment:B214/Talk About What You Want! 2/@comment-4547267-20140604051018/@comment-24866657-20140604100118

It would be normal for him to become larger at will, Tannin can do the same thing, for now Issei's body is dragon flesh so with some training (not on the same level as how he did with homing dragon shot) I think he can go ultraman again, it's just that he could only use Triana in that state because it consumes more stamina than usual.