Dark Foals - Knightbloom

On a night of drear and sorrow, the Sisters of Apple walked among the Ever Free Forest. The two were on the search for a mysterious sound they heard, so ghastly and void of life, that they were sure whatever made it had perished. Nonetheless, the two made it their duty to find the source of this wail. They traveled deep into the forest, the sunlight shrinking more and more with each step. Eventually they came upon a pool of water, made from a waterfall that crashed down on top of it. Below the fall stood a figure made of nothing but skulls and cloth.

The creature turned its gaze towards them, its visage turning the two pale as the moon herself.

"Pawns of Celestia, I beseech thee. Escape from my prison has left me tired and drained. You, old mare, grown and strong, will make thy recovery all the faster. While you, little filly, so young and pure, will be forged an unbreakable weapon to aid me in battle."

With that the monster pointed its long, bony fingers towards Applebloom and shot a bolt of light towards the young pony. With lightning speed her older sister Applejack leaped in front of the light and took it full blast. As the light made contact, it burst into a blinding white glow that enveloped the area in its brilliance. As it faded, Applebloom saw but a sword lying upon the ground; Applejack's hat beside it. The figure glided cross the water, a billow of fog cascading from its robes. It scoffed as it beheld its creation.

"Hmph...Foolish mortals and their sense of morals. This does little to hinder me."

As the demonic abomination reached a boney claw toward the sword's hilt, a brilliant flourish of color enveloped it. Try as it may, it couldn't lift the sword as bolt after bolt of magic blasted its body. The creature shrieked, making Applebloom feel as if her ears might bleed as it withdrew from its prize. With one final wail it wrapped itself within its tattered robes and vanished into shadows.

Applebloom stood there, shaking like a leaf from the shock of the ordeal as Princess Celestia slowly descended next to her. She pulled the frightened filly in close with a wing, Applebloom's body feeling cold as ice.

"I'm sorry for what has happened little Applebloom, but I cannot afford you much comfort. Time is of the essence."

Celestia stood, motioning for Applebloom to approach the sword forged from her sister's body. She reluctantly did as instructed and soon found she could lift the sword with little effort. It was so much larger than she was, yet felt light as a feather. Celestia nodded in approval.

"Your sister's soul lies trapped within this blade young one. Her loyalty to her family and unyielding resolve makes it nigh unusable by anyone but you. Even I, with all my magic and power, could never hope to lift it. It therefore falls to you to undo this wrong and set your sister free. It falls to you to save Equestria from its most terrible enemy yet! Do you accept?"