High School DxD is a light novel series written by Ichiei Ishibumi and illustrated by Miyama-Zero.
The series follows Issei Hyodo, a lecherous high school student attending Kuoh Academy who is killed on his first date.
The first arc, titled The Red Dragon Emperor's Awakening (赤龍帝覚醒 Sekiryūtei Kakusei), ran through the first two volumes.
The light novels also feature a series of side stories set in between the main storyline, and are often compiled into volumes.
A spinoff manga, called High School DxD: Asia and Koneko's Secret Contracts!?