This is the R18 version which includes adult sex scenes! Based on a BL fantasy manga by Kaziwara Io.

 One day, Toshiaki Gouzu (affectionately known as Gouzu)—a man who strays from society—is shot dead and somehow wakes up reincarnated in the world of a video game. Furthermore, standing before him is the game's last boss, the demon king Evelogia, whom he has always lusted after. The disillusioned and childish Gouzu stands there alone, quivering. He tells Eve "I fell in love with you," and without hesitation the courting begins.