How NOT to Summon a Demon Lord (Light Novel), Volume 7

"You fools who cannot even tell friend apart from foe—I have no reason to forgive your existences any longer!"
With Diablo learning of a ritual passed down by the Dark Elves that may be able to remove the remnants of the Demon Lord's soul still slumbering within Rem's body, he tags along despite her insistence to solve her personal problems on her own (out of concern of course—it has nothing to do with the Dark Elves having gigantic breasts according to the game! R-Right...?)