Luna pressed her ear against the door to her sister’s chambers, listening to her soft whimpering through the door. Mature alicorns went through heat once every hundred years. It was an intense time of sexual need and the one time when an alicorn was actually fertile. Most ponies assumed, incorrectly, that alicorns couldn’t have foals. Young alicorns went into heat every year but as they aged, their heat came less and less frequently. Unfortunately for Celestia, each heat was more intense than the last. As she heard another whimper from her sister, Luna couldn’t handle it anymore and pushed open the door, walking into her sister’s chambers.
It was frigid cold in her chambers. She had left all the windows open and the wind had brought in snow from outside. Her fireplace was cold and empty, and there were no blankets on her bed. Celestia laid shivering in the middle of her bed, her blankets on the floor.
“Sister!” Luna cried, trotting over to her worriedly.
She fired up her horn and closed all the windows. Then as she brought her sister into her hooves, she used her horn to light the fireplace and bring some wood from the wood pile. Her sister shivered in her hooves, opening her eyes slowly.
“L-Luna…?” She said, squinting her eyes to try and see the large blue form above her.
“I’m here, sister.” She said. “What do you think you’re doing, opening all the windows in the middle of winter and letting the fire die?”
“My heat…it’s so bad, Luna…” She said.
Celestia had rejected her suggestion a few days ago, but she had to bring it up again.
“Sister, you must take a guard.” She said. “Or any stallion who is willing. Your heat can’t go on like this.”
“That’s the problem, Luna.” She said. “There’s no stallion that wouldn’t be willing. I can’t trust them not to…not to…impregnate me… It would make them a prince if they successfully sired me a foal, and I’m not sure I could resist them.”
“A mare then.” She suggested.
Celestia shook her head firmly at that idea.
“Luna, giving your body to another pony requires implicit trust.” She said. “There is no mare I would trust with that…”
“What about Twilight?” She suggested. “You trust your her, do you not?”
“No.” Celestia said. “I can’t bring Twilight into this. I won’t.”
“And Cadance is married.” Luna mused.
Celestia lowered her head in defeat. Luna suddenly had an idea. She was sure her sister would reject it, but she decided to propose it anyway.
“What about…me?” She asked gently.
Celestia lifted her head and looked at her in surprise.
“I will do this for you, sister.” She said softly. “I love you, and you need me.”
“No.” She said, lowering her head again in sadness. “You’re my sister. I couldn’t possibly…”
“You don’t have to do anything.” She said. “Just lay there and let me please you.”
“No, Luna.” She said. “I can’t let you do this for me. I don’t…”
Luna suddenly stood up and walked back behind her. Celestia was lying on her side in the bed. She lifted her head and looked down at the lunar mare as she walked back behind her.
“Luna, what are you doing?” She asked.
“Shhhhhhhhh…” She said, reaching her muzzle down between her sister’s legs. “I’m going to take care of you…”
Celestia suddenly tensed as she felt her sister’s warm breath against her flower. A sudden feeling of dread nestled in the pit of her stomach as she realized what her sister was about to do.
“Let me see, sister.” She said.
Celestia had subconsciously pressed her legs together, trying to keep her sister from seeing her most vulnerable parts.
“No, Luna.” She said insistently.
“Shhhhhhhhh…just let me see…” She said again, using her hoof to spread her sister’s legs apart.
Celestia resisted, trying to keep her legs pressed together. Unfortunately, her heat had really taken it out of her and she didn’t have the strength to resist her sister. Luna forced her legs apart and stared at her flower, much to Celestia’s horror.
“Luna please…” She begged, hating the feelings of pleasure she got from another pony looking at her – even if that other pony was her own sister.
She suddenly felt Luna’s hooves on her barrel as she turned her onto her back. Celestia felt like a rag doll, unable to resist against her sister’s strong hooves. She still had control over one thing however and did everything in her power to keep her legs closed.
Luna was having none of that. She gently pried her sister’s legs apart and crawled on top of her, rubbing against her chest. Celestia couldn’t help but stare at the blue mare on top of her. She knew it was her sister, but she couldn’t help but see something…more too.
“Luna…” She said desperately.
“Shhhhhhhhh…” She said again, this time putting her hoof to her muzzle.
As she moved her hoof away, Celestia was going to say something but was immediately interrupted by the feeling of warm lips against her own. At first, she pulled back in shock, in total disbelief that her sister was kissing her. But the feeling of her warm lips felt so right in her lust-filled state, and she couldn’t help but return the kiss.
Luna suddenly broke the kiss, burying her muzzle in her sister’s neck as she nuzzled against her. As she started kissing along her neck and chest, Celestia finally found her words again.
“Luna, please.” She pleaded. “Please stop…”
Luna ignored her and continued kissing along her body, nibbling on the sensitive areas on the side of her neck.
“Please stop…” She pleaded again, hoping Luna would listen to her.
Celestia felt a sudden mix of relief and disappointment as Luna suddenly stopped and looked directly at her.
“Please, let me do this for you, sister.” She said. “All you have to do is relax and enjoy it. Just don’t push me away…”
“Please…” She pleaded. “You need this, sister and I-I want to…”
She blushed profusely, looking away.
“Y-you do?” Celestia asked in surprise, a blush covering her face as well.
Luna nodded sheepishly.
“But, Luna, we’re sisters…” She protested.
“I know…but you’re…very attractive, sister…” She said. “And it’s not like either of us are going to get pregnant from this…”
“Please, sister?” She asked. “You don’t have to do anything but lay there and enjoy it. I’ll take care of everything.”
There was a long moment of silence between them as Celestia thought.
“I-I’ve never been with a mare before…” Celestia confessed, finally breaking the silence.
“That doesn’t matter.” Luna said, sliding down her sister’s body. “You don’t have to do anything to me if you don’t want to. This is all about you…”
Celestia was still thinking about the situation she was in. She wasn’t sure about this. Her body was beyond desperate, but Luna was her sister. She was still cognizant enough not to want to risk complicating their relationship.
“This is just sex, sister.” She said, seemingly reading her mind. “We’ll still be sisters after this. Just let me help you…”
Celestia whimpered and adjusted her legs in discomfort.
“I…” She said.
Luna suddenly reached forward and licked along her inner thigh, making Celestia let out a small gasp in surprise. The situation was surreal to her, but she couldn’t deny that a part of her did want this. She looked down at Luna, who smirked at her reaction. Then without warning, she licked her inner thigh again, making the larger alicorn jerk in pleasure at the unexpected sensation.
“L-Luna…” She said in desperation, still at odds with the situation she found herself in.
“Shhhhhhh…” Luna said, nuzzling between her right thigh.
Luna slid her hoof close to her sister’s marehood, causing her to shift her body in a desperate attempt to prevent her from touching her most sensitive area.
“P-please, Luna…” She said, moaning desperately.
“Please what?” Luna asked, smirking once more.
Celestia wasn’t even sure anymore. She knew that she shouldn’t have sex with Luna but her resistance was waning with each passing moment. Luna licked much closer to her marehood this time, and she jerked in pleasure once more.
“Luna…” She said again.
“Tell me you want this, sister.” She said seductively. “Just tell me you want this and I’ll put out the fire.”
Celestia shifted her back legs again, her body screaming at her to agree. Her head was swimming with desire. Luna decided to take it a step further, kissing along the outside of her sister’s marehood.
“Ohhhh…Luna…” She breathed.
Luna continued kissing around her marehood, going in a random pattern as she got closer and closer to her prize. Eventually she dared to go even further, and gently traced the lips of her sister’s flower with her lips.
Celestia’s left leg kicked in surprise as she felt her sister touch her marehood for the first time. She felt a rock in the pit of her stomach as she felt pleasure from the contact and felt ashamed that she actually wanted more. Every muscle in her body tensed up the moment she felt her sister touch her. Sensing her tension, Luna went back to kissing around her marehood, moaning herself as she felt her own arousal levels rise.
Celestia looked down at her sister as she heard her moan. Luna wanted this. She was actually enjoying this! She felt her body relax as her sister continued her gentle ministrations. She subconsciously spread her legs further apart, giving her more room to work.
Luna could tell her sister was getting more comfortable with this and kissed her flower gently before kissing around the outside of her marehood again. Celestia tensed once more but relaxed more quickly that time. Luna kissed her flower again before going back to kissing around the outside of her marehood once more. They did this dance over and over again, and eventually Celestia stopped tensing up and got used to the feeling of her sister’s lips against her flower. Now that she was more comfortable with her actually touching her, Luna decided to take it a step further. She kissed her flower once more and focused on her clit, sucking it gently. Celestia cried out in pleasure at the sudden sensation, which brought a smile to her sister’s face.
She inhaled sharply as her sister went back to kissing around her marehood once more, expecting her to go for her clit again. But Luna wanted to go slowly, building her up to it before pushing her sister over the edge.
Celestia found herself silently begging her to kiss her flower again, growing impatient with the teasing. She shifted her body, groaning quietly in desire of her sister’s touch. Luna obliged, kissing her flower before pulling back a bit and licking along the outer lips of her marehood. Celestia jerked at the unexpected sensation before moaning in pleasure from her sister’s ministrations.
“Oh, Luna…” She said, moaning loudly. “Please…more…”
Luna smiled at her sister’s sudden eagerness and brought her lips in contact with her flower once more.
“Patience, sister…” She said.
Then without warning, she slid her tongue inside of her sister’s marehood, causing her to gasp loudly.
“Luna!” She exclaimed in surprise, looking down at her and putting her hoof on her abdomen right above her marehood.
The sensation was intense and unexpected, causing her to react by touching herself in surprise as her sister looked up from between her legs. She slid her tongue inside of her again, causing her to lean her head back in pleasure at the intense sensation.
“Mmmmmmm!” She moaned loudly, rubbing her lower abdomen to try and lessen the intense feeling of her sister’s tongue inside of her.
Luna gave her no respite however as she moved her tongue again, snaking it past her folds and deep inside her body as she smashed her nose against her marehood in her attempt to get as deep inside of her as possible.
“Ahhh!” Celestia exclaimed, the overwhelming sensation causing her to cry out.
In the back of her mind she was aware of the sounds of her sister’s tongue as she lapped at her dripping marehood. The whole situation seemed so surreal to her as she realized that she was having sex with her sister. Rational thought seemed impossible however, as Luna quickly pulled back before sucking on her clit again. The pleasure was just too intense.
“Mmmmmmmm!” She moaned again, this time pushing her sister’s muzzle away from her as her orgasm threatened to break.
Luna pushed her hoof away and held it against her inner thigh, lapping at her flower once more before sliding her tongue back inside of her again.
Celestia couldn’t take any more. The pleasure was way too intense. She felt like she was going to explode. She used her other hoof to try and push her sister away again. Luna defiantly trapped her other hoof against the inside of her other thigh, and pushed on both thighs at once, spreading her legs completely apart and pressing them against the mattress as she continued her relentless assault.
Her orgasm rapidly approaching and having no other hooves to use, Celestia could do nothing but hold on and endure the overwhelming sensation as her sister pushed her over the edge.
“Lunaaah – ahhhhhh – ahhhhhhhhhh!” She exclaimed, squeezing her eyes shut and throwing her head back, her entire body tensing up and shaking violently from the intensity of the sensation.
Luna continued through her orgasm, gently kissing her marehood as it convulsed in pleasure. Eventually Celestia’s orgasm died down and she laid limp on the bed, panting heavily. Her heat temporarily relieved, the gravity of what they’d done finally hit her.
“Shhhhhhhhh…” She said, crawling on top of her until they were muzzle to muzzle. “It’s okay, sister.”
She looked up at her sister and blushed before turning away.
“W-we just had sex, Luna…” She said.
Luna brought a hoof to her cheek, turning her head so she would look at her again. As she looked into her sister’s eyes, Celestia could see a sense of satisfaction in them.
“And it felt good, didn’t it?” She asked, smiling.
It wasn’t a smirk or a smile of bravado, but a caring, compassionate smile. Celestia opened her mouth to respond but took a few moments to find her words.
“Y-yes.” She admitted, sighing. “Yes, it did…thank you, Luna…”
Luna hugged her sister tightly.
“I’m glad I could help.” She said, murmuring in contentment.
Celestia wrapped her hooves around her sister in a loving embrace. She was still in an ethical dilemma, but Luna had definitely enjoyed it and she had too. Had they really done anything wrong? She smiled and closed her eyes, enjoying the feeling of her sister’s warm body against her. The moral and ethical dilemmas could wait.