'A whole army, ripe for the slaughter, and they're not even ponies! Quite the opposite, in fact. Your enemies are so much lesser than you, and when they pose a threat to these beloved friends and family of yours, what choice do you have? What choice indeed.'
Onyx lie curled up on his bed, clutching the sides of his skull.
'Such a waste. A withering kingdom, ruled by an incompetent monarch that cannot even keep her subjects fed. You could lead them, if only you had the will to do so.'
His hooves began to shake, and under his breath, he prayed for the light of day.
'Who do think will die first? Perhaps Winter Breeze will take a horn to the gut and spill herself all over the desert. Maybe Spellshaper will lose a limb and succumb to gangrene.'
Onyx could barely whisper into the dark night. "Please, h-help…"
'You'll want to keep your worthless guard alive, I imagine. I wonder if you'll succeed. Of course, there is one way to be sure. Are you strong enough to take that path? I wonder…'
The door to the hallway burst open, bringing with it a calming blue light. Borne on her outstretched wings, Luna glided into the room and landed at the edge of Onyx's bed. The glow of her horn grew brighter, illuminating the stallion that lie shivering on the red velvet bedspread. Her stomach lurched at the sight, and her tongue only loosened after great effort. "You need not fear, Onyx. I am here."
Onyx gasped for breath and snapped his head up to face the light at the tip of Luna's horn. He focused on it, the way it shimmered and changed hue every so slightly. The longer he kept himself transfixed, the further away the voice became, until all that remained was a shadow of a memory. He lie still for a moment, then sat up and whispered, "Thank you, auntie."
"Forgive my intrusion, but when I sensed your fear, I peered into your dreams." Luna sat down on the bed next to him. "You are… concerned for your Nightfall Guard's safety. I assure you, we have recruited only from the greatest masters of spells and swords. They will be most capable of protecting each other should your diplomatic mission fail."
"Auntie, it isn't just the changelings." Onyx kneaded the bedspread below him. "If something should happen and Sombra takes hold, I fear I won't be able to stop. I don't know what he'll force me to do. I might turn on my own troops or N–" His voice caught in his throat. A vision crossed his mind. White fur, stained red. "...or Noble. Please, auntie, you have such excellent control of Nightmare Moon. Help me lock Sombra away as well. Help me numb his influence over me. I don't care about the cost."
Luna gazed out at the cold room. Though Onyx's dwelling contained mostly fine luxuries, kept pristine through rigorous cleaning and organization, a small table remained littered with treasures from his past. His first lyre, on which he'd played a theme to make even Cadence smile. Black and white crystals from days spent joyfully practicing magic in the gardens. A love note from his first marefriend.
To the untrained eye, Luna remained stoic and unyielding, but to somepony that had known her for almost two decades, the signs were obvious. Her chest heaved almost imperceptibly with every breath. Her head hung slightly low. Her wings drooped a quarter-inch. "You… ask for sedation. What you seek will do you only harm. I shall not assist you."
Onyx leaned in, and his voice became more gruff and direct. "Auntie, all I ask is that you afford me the same protections you yourself have used, the same fortifications that you have placed on your mind and soul."
"What do you see what you look at me?"
"What?" Onyx withdrew a few inches. His lips parted and hung open while he searched for words. "I… you are a beautiful princess and a caring aunt that has always had my best interests in mind. I see a strong leader that deserves to be adored, one that I should model myself after." He scooted closer. "What do you see?"
"I see nothing."
Onyx shrank at the coldness of her tone. It gripped his heart, filling him with guilt and anxiety. As long as he could remember, Luna had never yelled at him, but the iciness in her voice had always sufficed.
Luna cast a sideways glance. "You seek to repress your nature, but it will not force Sombra away. All you would accomplish is the annihilation of yourself. I have been able to keep Nightmare Moon at bay, yes, at the expense of all the vibrancy in my life. I do not smile so much these days, nor have I allowed myself to cry since my return. I fear that allowing passion to take hold of me, even for a moment, would provide all the opportunity Nightmare Moon would need. She is under control, yes, but I would not wish this ennui, this smoldering nothingness, upon anyone. Therefore, I shall not assist you."
"Then you must promise me something else."
Luna cocked her head to the side. "Hm?"
"Should a time come when I am lost… If Sombra ever takes control of me, you must promise to destroy me."
Luna averted her gaze. "I cannot."
Onyx stood up on his bed. "But that's villainous!" He padded around Luna and began screaming directly at her face. "You have a duty to protect all of Equestria! Sombra threatens the well-being of your subjects, and you would sit idly by and do nothing? How? How can you argue that one meaningless unicorn is more important than stopping the reign of an evil tyrant?"
Luna closed her eyes. "Because you matter. Because I love you."
Onyx's eyes opened wide, and he took half a step back.
Luna took a long, calm breath and opened her eyes. "My dear Onyx, I could not possibly ransom your life for any sum." She shook her head. "I would be incapable. I would fail. Your value to me surpasses the threat of one thousand evils."
Onyx stared, suddenly feeling very small.
"Death and sedation are not so different. In either case, I would be trading away the happiness of somepony I love for uncertain safety. I would be sacrificing the young, talented colt I have seen grow into a great leader in the name of banishing the darkness for an unknown time. This, I cannot do. I cannot deny you the sweetness of life. It is only you that can truly defeat Sombra."
"But…" Onyx swallowed hard. "What happens if I can't stop?"
With a flash of movement, Luna reached out a foreleg, wrapped it around his neck, and pulled. Onyx could not react – he could only allow his auntie to draw him into her embrace. Her chest felt warm against his, and however briefly, she nuzzled him along his neck. "I shall always believe in you, Onyx. My faith shall not waiver for a moment."
"Ah…" Onyx tried to protest again, but he became lost in the warm feeling that spread from his chest to the rest of his body, from his hooves to the tip of his horn. It pushed back the cold emptiness of the room, and for the first time in years, the presence of Sombra seemed completely gone. In its place, Onyx imagined the countless faces of parents, princesses, guards, friends, and a brother of a different bloodline, smiling around him and viewing him not in the light of a former tyrant, but only as Onyx, a unicorn whom they cherished. He could feel their warmth as well, and the heaviness deep in his chest seemed to disappear.
For a moment, he understood. He did not feel like a reincarnation of a dead king. He felt like himself, a singular pony with beauty and flaws all his own. He saw himself on his own path, undeterred by the voices inside. For a moment, he saw clearly, and he felt free.
With a slow hoof, he reached around Luna's back and returned her embrace.