User blog comment:B214/Question and Answers 3/@comment-25222726-20140704190627/@comment-24098614-20140704212550

The Holy Lightning Dragon was discovered by the constant draining of Issei's power by Akeno sucking his fingers because Issei paid a price in that fight against Raiser because his arm turned into a Dragon's arm so the constant draining of his power into her created this power for her. The Extinguish Star was probably due to her training with Sirzechs but the move is far from being completed yet it still needs work.