Thank you *Bows*

When a monster absorbed their soul.their soul would be replaced with all the monsters evil. In the day they would be perfect. In the night they would be demons...

There was a side effect for humans though.....

After hundreds of years 6 human children fell down Mt.Ebbot, and 6 monsters were forever clean of evil.

The humans pitied the monsters and said if they absorbed a human soul they would forever be clean and never be evil again.