The best way to do it would be to give you a really long, super elaborate side quest to revive Aerith... only to find in the end that you can't and all your efforts were futile. If I were designing it, I would intentionally include a well hidden trail of secret breadcrumbs, gradually building hope as they were all followed, and then crushing that hope brutally once they reached the end of the line. Maybe I'd give them the reward of seeing a ghostly image of Aerith or something for a few seconds.

Cruel? Yes. Fun though ^_^