Strange things are happening around Canterlot High. So what else is new? A mysterious armor-clad figure protecting citizens from invisible monsters, that's what's new.
When rumors begin spreading that this nighttime warrior may be nothing more than a hoax, the HuMane 5 and Sunset Shimmer begin an investigation into the vigilante, but quickly uncover something far bigger than they had expected. Monsters from another universe are invading, reaching out from behind the mirrors…but through the darkness shines a helpful light. Is there a part for these six friends to play in this struggle against an unknown enemy attempting to conquer multiple worlds?

When you look in the mirror, what other than your reflection might be looking back?

(Kamen Rider Dragon Knight reaches into the Equestria Girls world.)
(Select Rider and attack names and powers suggested by MythrilMoth and KR Chrome.)
(This story is most conveniently read on Indented view instead of Double Spaced.)

Catch the non-canon spin-off: Kamen Rider × Kamen Rider EqG & Decade

 The universe has fallen into the crutches  of the Jark Matter Shogunate and the inhabitants cry out in sorrow. the last planet yet to be conquered, Earth. Jark Matters power has proven to be greater than the magical power of friendship blessed to 7 young girls. With the threat of the universe being trapped in the clutches of evil the earth has one last chance to fight...

Teenagers with attitude

Given the power of the stars, nine heroes make the last stand to free all 88 star systems. the rebellion has started among the cosmos, with a little luck and the power of friendship this team of unlikely heroes will become the shining stars everyone will look upon and give hope to.  

Our Friendship will take on the universe, KITA!

(Crossover of Uchuu sentai Kyuranger)

This story is a sequel to Power Rangers Guardians vs Power Rangers Revolution X

The Power Rangers are back! Now in their senior year of High School, the Rangers are hoping to have a peaceful time. But to their horror, a new threat has surfaced and is out to get them and take their Elements. To stop it, the Rangers must create new weapons, find new allies and defeat new foes. One thing's for sure, should they win, they will become legends.

This story is a sequel to Kamen Rider Unicorn

In this Hyper Battle Edition of "Kamen Rider Unicorn", Sunset Shimmer and Rainbow Dash have been working tirelessly as Kamen Riders Unicorn and Nasca to defend their home from the ever-increasing threat brought about by the arrival of the Gaia Memories, strange USB shaped devices capable of transforming the user into a terrifying monster called a Dopant.

However, when a new Dopant surfaces, stronger than anything they've ever faced before, will our heroes be able to summon the strength to vanquish this beast, or will Canterlot be razed to the ground?

"Time to restore Harmony!"

This story is a sequel to Kamen Rider Unicorn

Summer Vacation is still going strong for Team Unicorn, but every once and a while, even heroes need to take a break. And what better way than to play the hottest video game of the year?

However, this game becomes less fun when Canterlot City's youth contract a unknown disease that is slowly killing them. But when Sunset goes to confront this new threat, an enemy from the past returns to seek revenge on her, and on all the good in this and every world.

But hope arrives in the form of three renowned doctors and a game character - and one guy with a MAJOR god complex - who can help and stop this disease before it can progress.

Oh, and they also happen to be Kamen Riders!

< UNICORN! >

[+] MIGHTY ACTION X! [+]

Over a thousand years ago, ten Elements of Harmony were lost in another world. Now a group of young teens must come together, to protect this world form the evil that threatens it. With the help of the mane seven, they must become the Guardian Power Rangers.

Takes place after Legend of Everfree and in place of the next film.

This story is a sequel to Kamen Rider Unicorn

Sunset Shimmer has become burnt out after constant battles with Dopants and managing any magical mishaps that spring up. So after much deliberation, Sunset has decided to return to her home for a week long vacation.

However, evil doesn't take a vacation, and it springs up in Equestria. The organization known as Shocker, has set its sights on Equestria and threatens all that is good in the magical land. Fortunately, help appears in the form of the "Destroyer of Worlds", Kamen Rider Decade.

But what is Shocker's objective? Why have they targeted Equestria? Sunset Shimmer shall be tested like never before, against foes she has never encountered, see how her metal will be tested in Kamen Rider Unicorn's first movie debut!

Takes place during Kamen Rider Unicorn chapter Initiation

This story is a sequel to Power Rangers: Guardians of Harmony

When a new enemy from another universe threatens their world, the Guardian Rangers must team up with another set of Rangers to save the day. Can they pull it off, or will our world be taken over by this mad man?

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