Day-Shift
For all good things, there is a cost. You may have been gifted with the chance to fuck the goddess of the sun, but the price is pulling a double-shift.
You didn't get a chance to go home and dwell on what had happened the night before. Princess Celestia invited you into her bedroom to help her "scratch an itch". Turns out her itch was a need for some male companionship in the most intimate of ways.
But, rather than resting in your own bed, your commanding officer gave you the job of guarding Princess Luna's quarters as she sleeps. During the day.
It's still early morning, but you already know that this is gonna suck balls.
...
You chuckle at your own accidental joke. At least tonight your balls might get sucked. You grin and lean on your spear, fantasizing about what you'll do with Celestia tonight...
"Ahem."
You spin around, dropping your spear to the floor and scrambling to stand up straight. Your weapon may be lost, but this salute must be enacted no matter the cost. "Your Highness!" You smack your forehead with your saluting hoof a little too hard, causing you to flinch.
Princess Luna leans against the door frame closest to you and smirks. She, much like her sister, appears to undress herself before bed. With her sister in-mind, you can't help but examine her features: a soft face with hard, demanding blue eyes, a slim long body like her sibling's...
... A nice round flank...
She's much like her sister in many ways, but some of her specific features are more... abundant. With this in-mind, your willingness to guard this mare's room grows with every passing second!
... You realize that you've been looking her over and thinking about her body while she's stood here, staring into your eyes for almost half a minute now, smiling the whole time. She notices that you've changed your focus back to her eyes and decides to speak, "Are you done?"
You try to hide your embarrassment and recover, "Done guarding your room? No, a'am, I just started-"
Luna interrupts you with a hearty chuckle and changes the topic, "You're cute; I see why she likes you!"
Your eye twitches. Is she talking about...? You try to play it cool despite your fiery-red face, "Who likes me, a'am?"
She lifts a hoof and looks it over for blemishes, "Eh, nopony special. Just the mare you had sex with last night." You swallow loudly. "The mare who happens to be my sister and one of the rulers of Equestria." You shuffle uncomfortably, accidentally nudging your dropped spear in the process. How does she-? "You may be wondering how I know about this..." She looks up at you and frowns, "Nothing happens during my night without my knowledge."
You consider running away as an option. Maybe she'd let you off with a warning? Maybe you could escape before she reacts! Maybe-
She releases a cacophony of laughter, falling onto the far side of the door, "You should see the look on your face!" You really should, because you can't tell if you're even more panicked or merely flabbergasted. Luna recovers from her fit and proceeds to explain, "I'm not gonna punish you for it. If anything, I should thank you!" Your reaction hasn't changed. Luna nods her head into her room and steps inside, "Follow me; I'll explain."
Still terrified and confused, you obey her command and enter the room, which looks almost identical to Celestia's save for the wall's blue color and the lack of a fireplace and pillow in the corner. The fire is replaced by shelves of books and encyclopedias. You learn something new every day: Luna's a freakin' nerd!
The princess hops onto her bed (which you notice is about the size of Celestia's), then gestures for you to take a seat in the chair next to her nightstand. You sit in the indicated location and listen to what the mare has to say.
"Celestia's spent the last month using toys and everything she could to try and get off," Luna rolls onto her side and looks at the ceiling, "I tried my best to help her without directly interfering, but nothing was working. Then," she turns her head toward you, "you came in and saved the day (quite literally)." She pushes her front half up with her foreleg, maintaining eye-contact with you and gaining a curious expression, "So that got me thinking... how good at fucking could you possibly be to get my sister to cum for the first time in months?"
You can't figure out how to reply; you don't even know if you should! What do you say to that? Is she asking you to do her, or is she expecting a legitimate answer? You try your best, and you say the first thing that comes to your mind, "Pretty good, I guess?"
Luna stares at you blankly. Neither of you move a muscle, just gazing into each other's eyes. She's beautiful; on-par with, if not more so than Celestia. You can imagine her offering herself to you like her sister did, and sliding right into her. This is something you want. Now you just have to hope that she feels the same-
Your thoughts seem to be getting interrupted a lot. The princess lifts you with her magic, floating you over to the bed and just above her, holding you there while she flips onto her back so her belly is up toward you, her wings flattening against the mattress. She strips the armor off of you and tosses it aside; she smiles slyly, "Then let's put you to the test, shall we?" She carefully lowers you onto her, connecting your mouths and expanding your erection.
Your lips lock and your tongues begin their stampedes into the others' cavern, duking it out to gain dominance over the opposite territory. Her mouth feels like a warm summer night, complete with the hot breeze as she breathes.
Your cock gets uncomfortable as it presses into her pelvis, just above her vagina. She's a little larger than you, so you adjust your lower half to slowly rub your tip up and down her slit, causing her to hum softly. She returns the gesture, thrusting her lower half against your cock. Her wings slowly wrap around your back in a lover's embrace, and her mouth violently bombards yours as if trying to garner a greater reaction.
As your faces continue their vicious battle, you decide that Luna likes her sex a little rougher than Celestia, judging by the way she pulled you into this and the ferociousness of her advances. She wants more. She wants it hard and fast. She wants you inside her and cumming before she can say "By Celestia's beard!"
You're happy to oblige.
You ram your solid dick into her pussy, immediately slapping your skin together. You can feel Luna smile through her "Mph!" It's exactly what she wants, so you stay on-track. You pound her clit with all you've got, moving in and out with ferocity you didn't even know you had. With every slap of your waists, the mare gives another grunt, another moan, another hint of satisfaction. Eventually, she pulls her mouth from yours so she can breathe. A grin plasters her face; she is loving this!
You're not done with her face yet. While she takes a moment to survive, you begin planting kisses on her cheeks and neck, occasionally nibbling on her ear and garnering a giggle amongst her groans.
Slap, slap, slap, slap! You can feel your balls working their magic and beginning to fire their load. Your cum blasts into Luna's pussy, covering every surface inside with your nectar.
In-turn, Luna screams, blanketing your still-firing cock in her own juices.
You stop your brutal invasion, taking a moment to run your tongue from the bottom of her neck to the tip of her chin before you pull out and ruin her sheets with your natural glue.
The princess let's out a long, happy sigh, and you fall onto your side while you regain your energy.
Luna glances at you and grins, "I see how you did it now. You've got plans to go at it with my sister again tonight, right?" You nod, unable to really understand why she's asking the question, or how she knows that specific detail. "Alright; I have an idea to make it even better for you, but you're gonna have to get back to work standing outside my door before someone figures out why I was screaming." You reluctantly peel yourself from the now-stained sheets, putting your armor back on.
The mare sits up and folds her wings behind her back where they belong, "By the way," You turn to face her. "... thank you for that." She winks.
"Any time, your majesty."
Luna laughs, "Is that gonna be your catchphrase? Every time you fuck one of us you'll end with 'any time'?"
You realize that you said the same thing to Celestia when you'd finished with her. You chuckle, "Sure, why not?" You step out into the hall and shut the door when it finally hits you.
"Every time you fuck us."
...
You are so glad that you were given the day-shift.