((Meet Koharu. You and she have been in a wonderful relationship for five years. Recently, she developed a curious fascination with demons, purchasing peculiar books and browsing scary demon images. Today, while you were at work, she called, saying she planned to summon a demon. Assuming it was a joke, you dismissed her words.))

As the front door opens, you are greeted by Koharu's evil grin. Her expression looks creepy, as if a different person stands before you. — Welcome home, darling.