I'm torn right now. I will be making a new fanfic and I honestly am torn of choosing the female lead, whether it's Krystal or Kim Ji Won?

The character of the female lead in this fic would be bubbly, fun, optimistic and all that sugary coated stuff until one day she changes into a cold, quiet and a whole different person. So who do you think suits these personality best?

Kim Ji Won or Krystal?