Twilight Sparkle has come to accept what it means to be with both Princess Luna and Princess Celestia. Nightmare Moon and Daybreaker are a part the princesses, distinct but not entirely separate, and she loves them just as much as she loves their other halves.

Which is not to say they always see eye-to-eye. When the princesses decide to start a family, Nightmare Moon and Daybreaker decide to tweak the fertility magic - and the result is a much larger family than anyone anticipated.

Twilight, Celestia, and Luna have repeatedly done the impossible in defense of Equestria... but raising eighteen foals just might be too much for them.