How NOT to Summon a Demon Lord: Volume 12

Acting out the part of a Demon Lord, Diablo accepted a quest from the King of Lyferia. However, after befriending the kobolds he was meant to dispatch, he faces off against the Kingdom of Lyferia. But that situation is changed in the space of one night, because of a shocking decleration of war from the Empire of Gelmed! The enemy lays waste to a citadel city with overwhelmingly powerful Magimatic Sols, conquering it. Diablo, on the other hand, runs into an entirely different kind of crisis. “Erm… Diablo... I, uhm, saw it." "Huh?" “I saw what you… did in the courtyard with Solami… last night.” This is the twelfth volume of the adventures of an earth-shakingly powerful Demon Lord (or at least someone who acts like one) taking on another world! The start of a huge plot twist!

[From J-Novel Club]