This story is connected to Equestria's End

Spoilers for Aeon Legion: Labyrinth... and not much else.

Be warned, even the prologue and description have massive spoilers for Aeon Legion: Labyrinth

All other spoilers are on the level of "Twilight is an alicorn", "Snape kills Dumbledore", "Vader is Luke's dad",

The first four chapters are available for free here

Time travel has made the Edge of Time a dangerous place.

To protect the Edge of Time from devastation, the Aeon Legion seeks the greatest soldiers and warriors from across history. Those they deem worthy gain a chance to compete in the toughest training program ever designed at Aevum Academy.

Terra Mason does not know when to quit. Though consistently at the bottom of her class in every subject at Aevum, she managed to graduate with the best of the best. Though she is among the least experienced legionnaires, she has already faced down multiple temporal criminals, including the murderer of a Legendary Blade, and survived. Now, she continues her path to join the ranks of the other squires of Alya Silverwind as the greatest heroes of all Time.

Kairos has sworn to kill those who have used time travel for selfish purposes, acting as judge, jury, and executioner. The Legendary Blades are her main focus, yet her next target is Starlight Glimmer.

And Sunset Shimmer just happens to find this familiar.

Cover art modified from The Legion of Harmony - Master Starlight Glimmer by Aidelank
Despite the cover art being Starlight in pony form, there's only like 4.5 chapters with the characters as ponies

Crosses over primarily with Aeon Legion: Labyrinth by J.P. Beaubien (aka Terrible Writing Advice), but appearances from other time travel-related series are not off the table (anything from The Time Machine by H.G. Wells to Bill and Ted's Excellent Adventure)

I think this is the first Aeon Legion fanfic on the internet, which by default makes it the best. If you don't like that, then go read Aeon Legion: Labyrinth yourself and outdo me, but please, give me a link.