Twilight Sparkle not only mourns the loss of her library, but also questions her own existence as a library-turned-princess. The library not only housed many memories for her, but was also a part of her identity as a bookworm, and with the library destroyed, that part of her vanished forever.
She even starts thinking she has immortality, which means her friends will be next to die without her. One thousand years pass, and Twilight is still mourning the deaths of all of her friends while ruling Equestria. Unable to cope with their losses, Twilight kills Princesses Celestia, Luna, and Cadence as revenge for making her immortal, and reforms Equestria into an oppressive dictatorship. She builds conversion bureaus (not to be confused with the fanfic of the same name) that magically transforms every pony into copies of her friends, and makes them all live the same way as her friends, from living in the same kinds of houses, to having the same talents as them, and even voices and personalities!

She then travels back one thousand years into the past to kidnap her own friends and bring them to her time period. This eventually forces Twilight's past self and a slave from the future to head into the future, save her friends, and teach her future self about moving on with her life, even if it might mean killing her.