Hagure Yuusha no Isekai Bible: Isekai de Ecchi Manga Egaitetara, Seishozukai Toshite Agamerareteiru Ken Nitsuite.

When Suzuki, an unsuccessful erotic manga artist, was transported to another world, he used the power of his erotic manga to save the country of Daujin from economic crisis. After saving the country and becoming famous, Suzuki's erotic manga was praised as the "Holy Book" and he became revered as the "Holy Messenger". As the ero-manga craze swept across the world, the Demon Lord appeared in front of Suzuki, targeting his power. At first, Suzuki was afraid and confused, but the Demon Lord told him, "I want to spend my time creating, not fighting. I want to change the world with the power of books, not with military might." He listened the Demon Lord's true intentions, and decided to help...? (Source: MangaCross, translated)