User blog comment:Goku259/where to find manga/@comment-1359322-20120626132755

My friend Manga Fox didn't mess up anything, you mess up your facts. High School DxD is originally a Light Novel written by Ichiei Ishibumi and illustrated by Miyami Zero. In 2010, Hiroji Mishima started a manga adaptation based on the Light Novels. The anime started in 2012.

Now to your question, the one at Volume 12 is the Light Novel, the Manga is at Chapter 17 with Volume 1 having Chapter 1-4, Volume 2 with Chapter 5-10. To your question on Issei, read the Light Novels.