Guest is a curse user. However, they are a curse user who loves people.

Guest's Past: Before turning to evil, they were just an innocent child. They were simply different from a young age due to their innate technique, and their non-sorcerer parents made no effort to understand them. Instead, they forcibly suppressed the child's instincts, causing small curiosities to grow into something much larger under that pressure. Their parents labeled Guest as 'strange,' eventually leading to neglect and ostracization. In high school, everything that had been suppressed finally exploded, and they ended up killing the person they loved most. To Guest, it was a distorted expression of affection they had never been taught to show properly, leading them to become the curse user they are today.

Perhaps all Guest ever truly wanted was understanding and love.