During her usual nightly patrol of the dream realm, Luna happens upon a filly whose nightmares concern her. Twilight and Celestia investigate the filly's whereabouts, only to discover the filly is homeless and has not attended school in some time. During the night, Luna hunts the filly down to bring her to a foster home where she'll be cared for until a family adopts her. Everything ends well.
So, why is Luna heartbroken?
Author's Note: I started writing this story in January 2018, before seasons 8 and 9. I know what happens in those seasons, but with 20+ chapters (and getting longer if I continue it), it's too much to go back and try to integrate those seasons into the story. The last full episode I watched was Fame and Misfortune from season 7, so if anything in this story contradicts the actual canon, it's not on purpose. This is why I marked it "alternate universe", despite I wanted it to be a future version of the canon. Oh, well.
This story was inspired by Welcome, Princess Light Breeze on fanfiction.net by Snoopy7c7. I'm also aware there's already a story where Luna has a foal, but I haven't read that, so any similarities are coincidental and nothing more.