User blog comment:B214/General Discussion/@comment-27180505-20170331135923/@comment-120.188.7.245-20170401143030

Hmmm, in Vol2 Issei was shown to be in pain everytime his dragonified arm appeared and he wasn't able to use his dragonified arm. I don't think it was implied that it was due to Issei's stamina. Now, he is shown to be able to use his dragonified body at his own will (as shown when he punched a magician in vol 14), although he has some diffiiculties to return them to normal. So, i can assume that it has something to do with Issei's body, simply put the dragonified arm in vol 2 was not Issei's body but now it's Issei's body. Sure, Ddraig could turn Issei into something of a dragon, but it would not be Issei's body