Celestia have always had somepony to take care of.
first there was Luna, then Cadence and her latest Twilight Sparkle. But now when they are all grown up she can’t help but to feel both useless,lonely and old.
She knows that they will always love her and she will always love them, but one evening Celestia suffers from a nightmare and thus she begins to doubt whether her little ponies still want her around or not.
Her desire to have somepony to take care of slowly awakens a darker side of herself that she sealed away centuries ago.
In desperation she releases a criminal who once threatened to destroy Equestria. Celestia will stop at nothing to get her little ponies back, even at the cost of her own soul.

Crap. My original cover image won't upload. Link in the author's note.