User blog comment:B214/Question and Answers 3/@comment-25222726-20140704190627/@comment-1359322-20140705021346

Both move are actually an effect of sucking Issei's Dragon power. Akeno can form her element into an Asian Dragon shape. Rias' demonic power gain some Dragon trait, her Extinguished Star's attraction power to suck the enemy to her Extinguished Star and disintegrate themselves.