Jeanne is a girl who lives in our era's Earth in relative peace. Her life is thrown out of sorts when she's mysteriously teleported to MO's January world, where angels and demons once went to war.

The famed demon lord was supposedly vanquished hundreds of years ago. However, while wandering alone, she finds him living quietly in a warm cottage in the woods.

His stony red eyes subtly widen in surprise before he gently invites her in for tea, and ultimately a place to stay in this unfamiliar magical world.

[From official website]