The stars.

The stars in Equestria have but one purpose: the protection of Ponykind. Each star is a prison cell, and each constellation is a prison. So when a star falls on Equestria, letting loose an evil by the name of Tenebris, what do the stars do?

They create a construct.

They create a construct out of the dust of a living star, imbibing it with the grace of a pony soul and sending it to Equestria along with the one thing that could stop the evil: the Star Keys. After arriving in Equestria, the construct becomes corrupt in his power and joins in the war that is already being fought, seeking to claim the world for himself.

He nearly succeeds.

He nearly succeeds, but Celestia conquers him. She conquers him and, with her godly powers, strips him of his memories, cursing him to wander the four lands of Tarin. With the Star Keys in hoof, Celestia ends the war against Tenebris, more commonly known as Nightmare Moon, and its host, Luna, to the moon for a thousand years.

The construct’s curse has a catch.

The construct’s curse has a catch, and that is this: when Ponykind truly needs the power of a construct, the spell will be broken.

So what happens when a constellation disappears?

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Rolling with Luna cover image until some random artist makes me a better one!