There are many things a 15 year-old girl can do, but young duchess Charlotte de Constantia had no choice when she was chosen to rein in a living god: the isekai'd Hero, Tanaka Suzuki, who also happened to be her boyfriend.

Suzuki was immensely powerful. Enough to end a thousand-year demonic invasion, even. However, he's still a human with his own ideas of morality … ideas alien to the world he saved.

Ideas about abolition of slavery, for example.

The Powers That Be needed someone to control the Hero, because otherwise, they'd have to kill him. They were agitated. The slaves even more so. One wrong move, and a slave revolution would ignite—a civil war with countless innocent lives in the crossfire.

With tension so sharp in the air, Charlotte must use all her wits to find a bloodless way to end slavery, appease her nigh-almighty beloved, and make sure that everyone makes it out of this ordeal alive—all before the Thousand-Year War gets appended with the thousand first.