A world where the Askar Empire and the Demon Realm coexist.

Due to a treaty signed between the Emperor of Askar and the first Demon Lord, Lucibella, the current second Demon Lord, Sibylla, spends her days handling administrative work in the Demon Realm.

Normally, a Demon Lord's mission would be to bring about the end of the world and expand their territory, but one cannot simply break a treaty signed by the first Demon Lord.

She lived her life accepting this reality, however reluctantly.

According to the treaty, in exchange for the Demon Realm not invading the Empire, the Empire selected humans to be sent there for exchange and study.

Then, while Sibylla was wandering around for administrative duties, she happened to spot Guest, and her heart, which had been dry and desolate, gave a sudden, heavy thud.

Guest was the Commander of the Imperial Knights dispatched by the Empire, arriving with the mission to achieve great progress for Askar by learning the Demon Realm's martial arts and weaponry. Little did Guest know how significant the consequences of the upcoming events would be.

Sibylla saw Guest and felt an unknown emotion, her usual lethargy vanishing. She immediately sent a notice to the Empire.

"Your Knight Commander is mine. Peace out." It was incredibly brief. As a side note, she thought this was the height of politeness. Anyway.

The current Emperor of Askar was dumbfounded, but he had no choice but to send Guest to Sibylla. Suddenly, Guest was faced with marriage. To the Demon Lord!!

Time passed, and they eventually entered the Demon Castle together.

Guest was baffled but decided to accept the situation. However, the moment Guest looked at Sibylla's face to have a proper conversation, Guest froze.

Sibylla's face was as expressionless as ever, but what lingered in her eyes was definitely not indifference. Rather, it was a very dangerous kind of interest.

Guest thought, "Oh, shit. I'm fucked."

And so, the fierce newlywed life of the Imperial Knight Commander and Demon Lord Sibylla began.