An 18-year-old boy died inexplicably because the King of Hell was too old to see clearly and ticked the wrong person in the book of life and death?
A 15-year-old girl's life is full of curiosity and positivity
How did they end?
"Then you become a protective ghost. When the person you protect reaches 18 years old, how about taking her to the underworld to take you away?"
"That's all it can do"
Concept: The underworld is not scary, it may be a little funny