Across the multiverse, the Lord of Order Nabu could sense the dark presence of Equinox slowly gaining power in the magical land of Equestria, as the rogue sorcerer plotted to destroy the realm for his own mad goals. Sensing that it was time for a new champion, Nabu traveled to the peaceful realm in the form of the Helmet of Fate, an ancient relic imbued with limitless magical power.
After arriving in Equestria, Nabu surveyed the equine dimension in search of a worthy candidate to take on the duty of defeating Equinox. Nabu's eyes fell upon the talented cellist, Octavia Melody. Recognizing her stalwart spirit and devotion to her loved ones, the Lord of Order saw her potential, and the Helmet of Fate appeared before Octavia in a radiant burst of golden light as she was engrossed in her cello practice. Startled but unafraid, Octavia looked into Nabu's wise and ancient eyes.
"Wh…What are you?" Octavia gasped.
"I am Nabu, a Lord of Order. And I find myself in need of your help," Nabu declared, his voice gentle but firm. "Octavia Melody, the fate of all that exists lies in your hooves. You possess the potential to wield great magic and safeguard the balance of both your universe and all others."
Octavia blinked a few times, wondering if the floating, talking helmet in front of her was real. "Wait…protect? Is Equestria in danger?"
"Indeed," Nabu's tone became tinged with sorrow. "A being known as Equinox, a former agent of both the Lords of Order and Chaos who went rogue and plots to reshape the fabric of reality to suit his own idealistic vision of balance. He has arrived somewhere in your home realm, and his agenda threatens all of Equestria."
"But if Equestria is in trouble, why not get help from the princesses or the Elements of Harmony?" Octavia asked. "You say that you need my help? I-I'm just a cellist."
"Your music holds exceptional sway, Octavia Melody. It has touched the hearts of many and evokes emotions that foster connections and peace. But that musical talent is a product of your own inner spirit," Nabu clarified. "It is your balanced aura — a genuine equilibrium of order and chaos — that makes you the ideal bearer of my powers."
Octavia shook her head. "Wait a moment… I'm just a musician trying to make ends meet. I've never seen a day of battle in my life. What makes you think I'm capable of wielding magic? Let alone fighting some otherworldly villain?"
"Fate rarely calls upon us at a moment of our choosing, Octavia. If we do not take action now, Equinox's power and influence will only grow, and your home, your family, your friends: all of that will pay the price."
Octavia's spirits further sunk as she thought back to her parents and her friends in both Ponyville and Canterlot. And Vinyl…
"What say you?" Nabu inquired. "Will you accept the task of saving your realm from Equinox?"
Octavia stared at the floating magic helmet. She then glanced out at the horizon, where this Equinox being was planning Celestia-knows-what. Could she really just ignore the crisis before her, especially if there was something she could do to help stop it? A sense of urgency and resolve began blossoming within Octavia as she turned back to the ancient Helmet of Fate.
"Yes. For the sake of my friends, I do."
Octavia could've sworn she could make out the glimmer of a hopeful smile on the hemlet's surface. "Very well."
The helmet then hovered just above Octavia's mane, inviting her to don it. Reluctantly, Octavia grabbed the helmet and placed it over her head. In an instant, her whole body tingled with a warm sensation as the room glowed in a blinding light. Octavia could practically feel an ethereal magic flow through her veins. Her mind became bombarded with visions of cosmic beings and spells she wasn't remotely familiar with. She saw condensed scenes of epic battles fought by her predecessors, the countless lives they saved, and the eternal struggle of maintaining balance between the forces of good and evil.
As the light receded, Octavia found herself transformed into a completely different pony. Clad in magnificent armor adorned with ancient symbols, she held within her the powers of order and chaos. Octavia floated in the air in a meditative pose as the helmet's eyeholes glowed with blue energy. When she spoke next, Nabu's esoteric voice overlapped with her own.
"Arise, my new champion: Doctor Fate."


—This drawing is a direct sequel of my last one featuring Octavia's eventual rival, Equinox: https://www.deviantart.com/tfpandora/art/MLP-Symphony-of-Imbalance-Equinox-982640456