When a mysterious signal sent through the Cosmos is received and amplified by the Traveler, three Guardians are sent to investigate by orders of the Vanguard. Neither the Guardians nor the Vanguard could've known what to expect. The Guardians were told "prepare for anything".

They certainly didn't expect nor be prepared to find the world of Equis. What's more, Equis was long consumed by the Darkness. The Cabal Red Legion and the Fallen House of Bane have long besieged the world and have desolated much of it. Only the remnants of Equestria remain, and their Princesses captured and their magic seized.

Most would find it wise to run when faced with this.

Only...Guardians never run. They stand and fight
=========
Destiny crossover, with game/story elements characters from Destiny 2. Will have gore and swearing.