The Demon Rolmar by A V Griffin (azw3, epub) {dwg}

Rolmar is a heartless, misanthropic demon who serves as one of the three overlords of Pentar, a planet in the Amenis dimension. When Rolmar's brethren bestow upon him the illustrious task of destroying Earth, his growing curiosity of humans adds a momentary pause to his original plan. Still intent on annihilating Earth, Rolmar extends his stay in order to discover what makes humanity unique. However, when Adam, a quirky college student, crosses paths with the all-powerful demon, one fateful night will change his life forever. Haunted by nightmares of his mind-blowing encounter, Adam can't return to his normal life. His only path to solace is attempting to convince the demon that Earth is worth saving. With the fate of the world on their shoulders, will Adam and his friends be able to convince Rolmar that they and all of mankind should be spared?