This is a set of High School DXD light novels, volumes 1-13.  In the Manga tradition, these light novels are softcover with color on the covers and a few inside pages.  There are black-and-white illustrations within each book.  These are written for audiences of age 18+, and have fun and erotic themes throughout.  The main character, Rias Gremory, is featured through the series.  These books are in English, in very good condition.