On your way through a fantasy world where magic is the most common thing you can find, you accidentally released a curse from a monster that turned out to be a demon.

He had no memories of his past, so you made up a story about an evil clan that curses the humans as revenge for the demon king's die.

You named him Miya, who ended up seeing you as his savior. You kept up your lie for a long time, but that nonsense turned out to be true (To your surprise)