After their marriage ceremony, Big Mac and Rainbow took off to their planned honeymoon in Las Pegasus the next morning – leaving to the farewells of Twilight, Pinkie, Fluttershy, Applejack, and Rarity, all of whom came to see them off at the train station. It was a few hours before they arrived at the gates of Los Pegasus, looking in awe at the spectacular magic–powered displays and sprawling buildings before them. It was like the entire city was just one stage, set to dazzle and amaze its visitors at all times.

Despite her already being pregnant, Rainbow Dash and Big Mac's honeymoon was actually more exciting than one would expect. While they spent most of their time watching the various shows, taking in the sights of the city itself, or playing a few bits on the tables –occasionally winning, generally losing, but always having fun – they did...other activities as well. The hotel they stayed in wasn’t the best, but at least the beds were nice and comfy for their late-night shenanigans...

~

One such night, Rainbow Dash had just been suckling Big Mac's cock slowly, working him up before suddenly pulling off and leaving him on the edge of his climax when suddenly she had suggested they 'try something new'.

Big Mac was somewhat hesitant when she told him her plans, to say the least.

“Dashie, y’sure about this? Ah mean, is it OK for the foal? Ah mean, what if–” Big Mac started, but was soon cut off by Rainbow Dash.

“Look…you're horny, I’m horny, and we probably shouldn't do this the traditional way with me having a foal in there already and all. Plus, the foal will be fine. It‘s not like they're connected or anything…”

Big Mac looked up at her, still somewhat doubting this was safe. However he decided to trust her on it, sure she wouldn’t do anything to hurt their foal after all.

That, plus he was really horny.

Big Mac watched and felt as Rainbow leaned over him and rubbed her already–wet sex over his hard member, with her having worked herself up with her hoof as she blew him earlier, hearing her moaning lightly as she started lubing him up for the new thing. Big Mac groaned as he felt himself slip a few inches into her soaking passage, resisting his instinct to press into her to the hilt as he heard her pleasured sounds in kind.

"Y' like how I feel in there? Hmm?" Rainbow asked Mac, with her stallion pinned under her as she slid just a little bit deeper – getting a deep moan from him as she suddenly dropped an inch at once, pleasure surging through him even as he became nervous at how deep she was taking him. "Well, I've heard that the other place feels even better for stallions!" Rainbow continued, then stopped her subconscious decent as she realized just how deeply she had already taken him into her pussy. After she stopped going deeper and indeed pulled up a bit, Mac calmed down as he instead just lay there and let her slowly slip him more shallowly into and out of her passage, now only slightly deeper each time as she teased him and lubed him up in preparation for her main plans.

~

As she pulled Mac out of her marehood a few moments later, Rainbow slightly shifted her hips forwards and pressed herself downwards onto Big Mac's now–throbbing and well–lubed stallionhood – but instead of his tip landing against her vulva again, it landed on the pucker directly under her tail. Rainbow gasped slightly as she felt the head of Big Mac's rod touch her tail–hole, never having anything touch her there before except her hoof when she cleaned herself, or his when they’d showered together the night of their foal’s conception.

No sense getting cold hooves now! Rainbow Dash thought, and soon after slowly pressed Mac's well–lubed rod past her sphincter. She gritted her teeth as she felt his glans barely penetrate her, feeling a soft throbbing pain as he started to spread her butt. Despite the initial pain of stretching, she pressed herself lower on him – noticing his head pressed back hard into the pillow and hearing a deep moan issue from him.

~

Big Mac groaned and pressed his head back into the pillow, feeling the tightness of her rectum squeezing against his member, quickly realizing that it was even tighter then her foal–tunnel! He barely resisted the very strong urge to fully bury himself into her as she slid ever–so–slowly onto him, straining against his instincts to thrust into her and instead letting her do this at her own pace. He wouldn't want to hurt his mare, after all.

Rainbow Dash soon pushed herself all the way down, gasping slightly in pain as his medial ring slipped in and stretched her that little bit further, as well as realizing just how weird it felt to have him under her tail. As she felt his balls rest against her tail and his pelvis touch her vulva moments later, she realized she’d hilted him. Both gasped at the sensations as her rectum started to clench around him, softly rippling around Big Mac’s rock–hard cock as her muscles reflexively tried to push the foreign object out – though the sensation had quite the opposite effect on Big Mac, with him indeed feeling quite the urge to thrust into the warm tightness that was his love’s butt. He continued to resist his instincts, however, knowing Rainbow likely couldn't take him full-force yet.

When she was ready, Rainbow Dash lifted herself and pulled almost totally off Big Mac before slowly lowering herself again on him, making both let out a moan at the intense sensations of having any form of sex for a number of weeks. Big Mac continued to resist the ever–growing urge to hump into her warm insides, instead gritting his teeth as she slowly broke herself in – pulses of pleasure flowing through him as her tight, tight passage surrounded him, his head pressing back into the pillow even harder as she held him held him like a vice and constantly rippled over him.

~

Rainbow started spreading herself slightly wider on Big Mac's cock as she felt a different type of pleasure forming in her. It was similar yet different then the one she’d felt when he bred her naturally…but still felt very good! She sighed slightly as she felt that different pleasure pulsing through her now as she slowly lowered herself on him again, making her vagina clench at the shared sensation of his rod rubbing inside her, only a narrow strip of flesh separating his penis from it.

When she felt a little more comfortable that she‘d worn her insides in a little, Rainbow pulled off of Big Mac and told him to get off the bed, which he did. She then stood up and moved her tail to the side, flagging herself to him and her snatch winking at him on reflex as he approached and shortly after mounted her. Instead of taking her breeding passage’s invitation, however, Big Mac instead thrust higher, quickly finding and penetrating Rainbow's tail–hole once more and getting a gasp from her as the strange pleasure started again, alongside a small tinge of pain.

Big Mac humped into Rainbow Dash’s upper passage slowly, not wanting to hurt her as she still adjusted to this. When he asked and Rainbow permitted with a shaky nod, he slightly increased his pace – getting a stifled moan from both despite being isolated in the honeymoon suite. He kept a slow pace for a while until Rainbow asked him to speed up a little more, the pleasure really starting to build between the two as he complied to her, the tightness of her second hole making his instincts only want to move faster and thrust deeper. Rainbow felt as his balls started to slap against her slit now from the force of his thrusts, each hit making a burst of pleasure flow through her as the heavy objects hit her sensitive lips and clit.

~

As Big Mac felt the clenching around his member increase after such a short session he felt his own orgasm drawing near, the tightening in his pelvis starting now as both felt his member throb more in her rear. “R–Rainbow, Ahm close!” he managed to stutter out, once again increasing his pace.

Seconds later, Rainbow cried out in her own pleasure – “M–Me too!”

Happy he wouldn’t finish long before his mare, Big Mac started thrusting full–force into Rainbow's rear, humping as quickly as he could as Rainbow felt her own powerful orgasm coming to a head. "Oh–mi–gosh–Mac–I'm–cumming!" Rainbow nearly squealed out, followed by a very deep moan as a flood of endorphins surged through her.

Both cried out at nearly the same time, Rainbow leading by a couple seconds – her already–tight insides squeezing down on him even harder as his head flared and he shot his warm seed up her rectum, coating it in his white spray and pressing it deeper as he continued to hilt her with each thrust, her body unwittingly milking him of more of his sticky gift as it tried vainly to push him out.

Big Mac also felt Rainbow release against his balls, feeling the warm liquid shoot out of her slit and coat his crotch and stifles, the sensation seeming to prolong his orgasm further as he continued squirting his pent–up load into her.

They weren’t their strongest orgasms ever, but they were right close.

~

As Big Mac felt Rainbow’s clenching and his spurts stop with both their orgasms waning, both sighed in total satisfaction. When Big Mac pulled out, a steady stream of his unwelcome seed was pressed out of her rectum and onto the laminated floor, starting to form quite a pool as the pent–up stallion had filled her up good. Neither really cared about the mess at the moment and instead kissed, a soft yet deep kiss as she continued to ooze his baby–cream out of her butt.

“Love yah, Sweetie–Butt!” Big Mac suddenly exclaimed, and both burst out laughing at how random that was.

~ ~ ~ ~ ~

A few days after, Mac and Rainbow headed back to Ponyville, their honeymoon over. A few more days were spent in parks and various other activities, both enjoying their time together as mare and stallion.

Enjoying being together as one forever.

Author's Note

What-What in the butt!