Some time has passed since the end of the Friendship Games, and Twilight Sparkle is still adjusting, but it's nothing that Sunset can't help her with. However, something seems off when Twilight starts to have dreams. Dreams of a library with infinite books, and of a masked warrior who fought against monsters.
It is soon revealed that these were not dreams but premonitions, the power of the Earth has give birth to the creations known as Gaia Memories, and in order stop those who would use their power to hurt others, Sunset and Twilight will have to work together to stop it. With knowledge in hand, Twilight will equip Sunset with the tools needed to fight this menace, Sunset Shimmer will become Kamen Rider Unicorn!
"Time to restore harmony!"
< UNICORN! >
This is a crossover of the Japanese Tokukatsu type TV series, Kamen Rider W
Apparently it has a TV Tropes page, go figure. Thanks whoever did it!
New cover art is fan art from pyropyre
And here's the theme song, Brave Phoenix
Made this to help with reading: Kamen Rider Unicorn Reading Order