My childhood friend, who I thought was dead, had become the Demon King.

Lucia, the main character, who lives peacefully with her lover Ortho , one day while taking care of the children as a sister.
Ortho finally proposes to her, but Lucia can’t forget her childhood friend Nero, who was chosen as a hero about seven years ago.
On that day, seven years later, she finally replied to Ortho and wanted to start living a positive life..
Lucia, who followed the figure to the outskirts of the city alone, fainted before she knew it. When she woke up, she  found Nero in a strange room who had grown and  become a demon king. It is a story about being cuckolded by your childhood friend  and having sex because he is obsessed with you now