Princess Luna, always clad in her gleaming regal armour… looked anything but as she paced around in her chambers. Her shimmering mane was frayed at the ends, dark bags hung under her reddened eyes, and her coat was given to a feral-like fuzz. She was mumbling something to herself as she paced, and a slight shiver ran up and down her spine now and then.

This was not the reason she was pacing. That which confounded and panicked her was something deeply internal. For you see- whether you believe the Nightmare to be a self conjuration or not- transformation magicks had a way of imposing themselves on the user, permanently, in often mysterious ways.

Indeed if one looked closely at our ragged Princess of the Moon one would notice that something gleamed in her mouth, shinier than the rest of her teeth. The moons light almost seemed tripled in intensity and sparkled off them

Fangs.

Ever since her first dance with the demons inside her she had a… craving. A craving that came now and then, and until recently she had been more than willing to simply call in one of her loyal Threstral guards and sup as she would.

Much had changed since then, and Luna had gone from embracing her demons to trying to best them. Presently that was indeed what she was doing, trying to ignore the craving; the insatiable need to feast on the lifeblood of a pony.

So in her chambers she had been, for days, knowing not sleep nor food, only allowing herself tea and bread.  Her sister worried, and knocked on the door once again.

Luna swallowed, collected herself, and spoke as confidently as she was able.

“Si- sister. We are fine, we merely… have a cold,” Luna spoke, unable to hide a quiver in her voice, and gave a mocking cough.

Celestia replied from across the doorway, her voice muffled by both wood and the magical field preventing her entry.

“Luna, you haven’t been able to lie to me since we were foals. Please, let me in- I want to help.”

For a moment it looked like Luna might relent, willpower fading and her face softening from the scowl she wore as another shiver ran down her spine- but that very shiver emboldened her. How could her sister, her loving and caring sister who had brought her back even after all she had done, know of the evil she still possessed?

“No.” Luna said simply.

Celestia was not dissauded so easily, and outside in the hall she sighed before her horn began to glow a brilliant gold. It lit the darkened hallway and filed it with perfect daylight before sending forth tendrils of power. Luna’s blue magic sealed the door, but in her exhausted state it was no match for Celestia’s power. It only took a few minutes of fight for her magic to push aside Luna’s, and upon finding the door locked, she simply burned it down.
So there Celestia stood, with the smoldering doorway ahead of her and her weakened sister staring back at her beyond. Celestia, the image of health and vitality, of feminine beauty and perfect form. She strode into the room, caring not for the burning embers that rained down from the doorway or the glowing hot stones on the floor, and looked towards Luna with a worried expression on her soft face.

“You look ill, Luna,” She said simply, and slowly approached her sister.

Luna looked away, but was far too weak to run or teleport. She was trapped, and it was only a matter of time. “I am… fine, sister. Truly. I need only rest.”

Celestia stood before her, a good head taller than her sister, and frowned as she put a hoof to her chin, gazing into her turquoise eyes. They were far less seductive than they were normally, almost pale.

“You are lying, Luna. Do I need to remind you of the last time you hid something from me? I’m your sister- I love you- tell me what is wrong.” Celestia pleaded.

Luna sighed, and swallowed her nerves before looking into Celestia’s eyes. When she spoke, her fangs shone brilliantly in the moonlight, revealing themselves immediately.

“I am… not as reformed as you may think, sister. I fear that my corruption will shadow me until the day I depart this world,” she said, and brushed Celestia’s hoof away, standing to turn away and stare into her moon.

“You do not know what it is like to… crave, what I crave. It is monstrous, terrible- and yet…” she glanced back at Celestia, with a deep sadness and shame upon her pale face.

“It is me.”

Celestia had no fear or anger- only a deep sense of love and caring as she looked towards Luna. “Tell me, Luna- specifically- what is it you crave?”

Luna spoke simply: “Blood.”

Luna walked back to her sister, slowly and seemingly ready to collapse as she did. “Not the blood of mere cattle or even that which a doctor might have. I require fresh, warm, blood from a pony. I remember a time when I would drain my own guards half to death to sate myself- but I do not wish to be sated. It gave me a great thrill of power that they would willingly give themselves to me- but no longer do I wish such things. I just want… ” She sighed, deeply, and flopped down before Celestia, spread out upon her hooves and even letting her wings relax and unfold.

“I want to live in peace, just as a mare. I tire of darkness and moonlight, I want… sunshine.”

To that Celestia smiled, and removed her shoe so that she could stroke the back of Luna’s head with her hoof. So soft and gentle, and she leaned down as she did towards Luna’s ear, blushing slightly and smiling.

“I think that can be arranged,” Celestia whispered, and lowered herself to lay beside her sister. She nuzzled her head under wing and wiggled so that her slender, soft, neck was mere inches away from Luna’s face.

Luna, meanwhile, looked away. A flush grew on her face, a bright red that contrasted against her haggard looking appearance. Her heart sped up and thumped in her chest and she desperately appealed against her body even as she licked her fangs, so close… so close.

Without even really thinking about it Luna turned and snapped her jaw open, brandishing those fangs with a quiet hiss before sinking them into Celestia’s neck with a powerful stab. Her eyes rolled back into her head and she groaned deeply as contact was made with her sisters arteries, and her sister in turn made a rather high pitched squeak. Celestia shuddered, the pain was an odd sort. A sharp stabbing pain on her neck, but love and care for Luna dulled it. The odd sensation of internal suction was interesting as well, almost… pleasurable. She blushed greatly and hid her face under Luna’s wing for the moment.

While Luna’s eyes rolled back into her head and she experienced the fulfilling ecstasy of feeding, her fangs began to draw from Celestia’s bloodstream while her body shifted into feeding mode. Her heart beat steadied around Celestia’s own for a time, and the fluid pressure of Celestia’s bloodstream fed itself into Luna. Her throat pulsed rhythmically as she fed, and the effect on her appearance was notable immediately. The colour came back to her face, and her mane regained it’s beautiful appearance.

Celestia laid there in a blissful state, feeling as matronly as could be as she allowed Luna to heal herself from her own life juices. It was such an amazing feeling of compassion and care. To know that she could provide for her sister in such an intimate and loving way made her heart race in her chest. She nuzzled against Luna, rubbing her chin against her side lovingly while her great wing swept over and pulled Luna tightly against her. Celestia could even hear, and feel, the heart of her sister which gained in strength over the slow minutes.

Princess Luna then opened her eyes, wide and alert as they suddenly appeared to have a monstrous slit in the middle. Glowing brightly in the dark she blinked as her heart sped up and the feeling of overwhelming power, the feeling of having another being so vulnerable before her, swept through her. If she bit a little deeper she could have everything she had ever wanted… Equestria would be hers and she could fill herself with the life fluids of her sister. Her sister whom had everything, beauty and intelligence, and a radiant smile that attracted stallions and mares to follow her. It could all be hers…

Luna gasped and withdrew her fangs, blood dripping on Celestia’s coat before she licked frantically at the wound to seal it. Her breaths came in ragged gasps as she fought to control herself, and her eyes regained their natural vivid appearance. She quickly stood and tore her gaze away from her sister as she laid there on her back. So… vulnerable…

“I am sorry,” Luna spoke at last, breaking the silence.

“Mmm… don’t be,” Celestia replied, her voice soft and lazy as she continued to lay there. “You can’t help who you are.”

“/what/ I am,” Luna corrected.
Celestia giggled and rolled over, slowly coming to her hooves and then striding towards Luna. She quickly placed her wing around and pressed her sister against herself in a loving embrace.

“What you are, Luna, is my sister. Perhaps the pony I care for most in this world. I would do anything for you, and if this is what you require- than I will provide.” She said, her voice soft and loving.

“You will?” Luna asked, tilting her head to look up at her sister. Her eyes fixated on her neck- but she was sated, for now.

“Of course. I… love you, after all.” Celestia replied, a sharp blush coming to her face while she spoke and her brain suddenly becoming muddled with a burst of emotion. Something was different when she looked down at Luna- something had changed.

Celestia leaned down, blush across her face, and kissed Luna. Right on the lips, a silent and passionate kiss that sent Luna’s eyes wide and an equal blush glowing on her blue face. When Celestia pulled away she glanced to the side, and coughed.

“How often does this happen?” She asked.

“It depends… but normally once a week. We have been trying to avoid it for some time.”

Celestia nodded, and strode towards the door. She glanced back at Luna before departing, with a great smile on her face. “Until next week then, Luna… I look forward to it.”