Younger Childhood Friend Demon Lord x Engaged Protagonist
The main character, Lucia, lives peacefully with her lover Ort while taking care of the children as a sister.
Ort finally proposed to her, but Lucia couldn't forget her childhood friend, Nero, who was chosen as a hero about seven years ago.
Seven years later, on that day, I finally replied to Ort to start living positively, but...

Mamono appears in a city that has been protected for a long time.
Lucia chases him to the outskirts of town alone, and before she knows it, she faints.

When I woke up, I found Nero, who had grown up to become a demon lord, in an unfamiliar room.

It's a story about sleeping with a fiancé and having sex with her obsession.