User blog comment:B214/Question and Answers 4/@comment-24866657-20141019162746/@comment-24866657-20141020103325

I think somehow I find out the answer.

It's said that Great Red created the exact body of Issei right? Since he was a devil to begin with therefore Great Red must have including demonic energy when he recreated Issei's new body too, so technically Issei's new body was not a humanoid dragon but demoniod dragon. Or a humanoid dragon with demonic energy inside him.