How NOT to Summon a Demon Lord (Manga) Vol. 6

All her life, Rem has carried the soul of the demon lord Krebskulm inside of her, terrified of letting such an evil loose on the world. But now a mysterious Fallen has told Diablo, Rem, and Shera about a ritual that could free Rem. The catch is that it means letting Krebskulm free as well... Can Diablo, a fake demon lord from the ordinary world, take on the real deal?!