User blog comment:B214/Question and Answers 2/@comment-3965848-20140203220442/@comment-24098614-20140203221339

The thing you mentioned happened in Volume 5 when Issei was training with Tannin because he showed Issei how to breath fire in fact it is one of the basics you must learn to be a Dragon, and this was taught first with a lot of other things check this out in Volume 5 of the Light Novels