“Big Bro! Big Bro! I got my cutie mark!” Rainboomer ran up to his big brother, gibbering non-stop. “I got it! I got it!”

Blaze caught him an enthusiastic hug... or, rather, he was caught by Boomie's unerring rush. “Hey there, Little Bro! Come on, let me see it.”

Boomie dropped to the floor and turned sideways to show it off. Brand new and still sparkling, a circular rainbow that looked exactly like the one he'd just made in the sky above Cloudsdale. “I got it by doing a rainboom! Just like you said I would! Just like Dash did!”

He smiled and tussled his little brother's rainbow hair. “Way to go, little guy! I bet you're excited.”

Boomie shot up, straight through their home's cloud roof, leaving a rainbow trail in his wake... only to reappear moments later. “I've never been so excited in all my life!”

“Good for you, bro. Good for you.” Blaze looked out the gauzy cloud window for a moment, thinking. “Hm, you know, I'm about to go pick Rainbow Dash up from her flying practice. Why don't you come with me?”

Boomie paused. This was strange. “But you've never wanted me to go with you to pick her up before...?”

“Well, you've never had a cutie mark before.”

That was fair enough, Boomie supposed, even though he wasn't sure what that had to do with anything. Still, he only just got his cutie mark... how was he supposed to know what changes having one might mean? “Okay.”

“Good. Come on.”

The two of them trotted out into Cloudsdale together, but Blaze slowed as they went down mist street, falling back a little to be closer to Boomie. “Now that you've got your mark...”

“Yes?” Boomie could hardly contain himself. This was so exciting! So many changes!

Blaze chuckled at his enthusiasm. “Since you've got your cutie mark, you'll be considered an adult now, so you can expect to be learning a lot of adult things.”

“Ooh! Like what?”

“Well, most importantly, you're going to have to learn how to take care of your mares.”

Boomie almost stumbled against the puffy street after hearing that. Somehow, he'd never realized until now what getting a cutie mark would really mean. “My mares?”

Blaze nodded. “Yes, yours. Now that you've got your mark, the Princess of Love will be giving you your very own mares to take care of soon. It's a big responsibility.”

They walked together in silence for a moment, Boomie thinking about what that would mean.

“Plus,” Blaze eventually continued, “I'll be glad for the help in taking care of Dad's mares and my own, especially with heat season coming up.”

Boomie considered that for a moment. “But why are you taking care of Dad's mares anyway? Can't he do it?”

“Well, without getting into the details of it...” Blaze paused. “I guess I have to get into the details of it a little bit. Dad's getting older, you know... he can't really get hard enough to do it anymore.”

“Oh.” Boomie wasn't sure what that meant, but he didn't want to look like a big dumb-dumb in front of his brother.

“What you need to know about mares is that they have powerful needs, and it's our responsibility to make sure they get their needs fulfilled.” Blaze looked back at his brother. “They always want it, but especially during heat season. Stallions own mares the way they do in order to make sure they get taken care of as well as possible. It's an ancient system set down by Princess Celestia herself. The mares are happy with it – they couldn't stand to be alone, and there aren't enough stallions to go around. That's why every stallion has his own group of mares to take care of.”

As they walked, they came upon a stallion and a trio of mares. The stallion was leaning against a puff of cloud, and all three mares were licking his private parts, nuzzling their faces into his crotch.

“Ah, perfect.” Blaze pointed at them. “You can see those mares are loving their stallion. If we watch for a moment, I bet we'll see them... yep!”

One of the mares pushed the other two away and sat down on the stallion's lap. She wiggled back and forth and the stallions private parts went inside the mare's. Boomie watched, wide-eyed. He'd seen stallions and mares going at it in public like this plenty of times before, but he'd never paid much attention to it. Now, though... now it seemed much more important. He'd be expected to do the same thing soon!

The other two mares tried to pull the first off, but she gripped her stallion tightly, whimpering as she rocked her hips back and forth rapidly. When they failed to pry their companion loose, their attention turned to Blaze and Boomie. Their eyes looked strangely hungry, and one of them let her tongue loll out.

“We'd better be going, Bro.” Blaze nudged him on. “We need to save our energy for Dash... and we don't want to be late for her.”

Boomie nodded and followed his brother along.

“Now, Boomie... You should know that flying practice and all that exercise gets Dashie pretty worked up. I usually need to take care of her right then and there when I pick her up. You gonna be okay with that?”

“Um... I guess?”

“Good.” Blaze grinned over at his brother. “Because... well, since you need to start learning about these things, I was thinking of having you participate a little.”

Boomie's eyes went wide. Participate? Was he really ready for that? Sure, he'd looked at mares sometimes, and even begun to get pretty interested in them at times. But the thought that within mere minutes he could be doing things with them... that was a heady feeling. He'd seen Dash before, of course, growing up together. He'd even seen Blaze humping away at her... but he'd been too shy to go and get an up-close look or ask about it. Besides, he'd been told lots of times that such things weren't for foals. But ... he wasn't a foal anymore.

Before he could fully come to terms with what would probably soon happen, they arrived at the practice grounds, a huge flat section of cloud with lots of open space, plus a few obstacle courses laid out through it.

He looked around, searching, and quickly spotted her. The family trait of rainbow manes had her leaving a rainbow trail behind her that was easy to spot.

“Rainbow Dash!” Blaze called out. “Dashie! Come on, it's time to go home!”

She came zooming in, straight for him, her eyes fixed on him and a huge grin on her face. There was no way she was going to stop in time!

Of course, she wasn't trying to stop in time. She plunged right onto Blaze and tackled him to the soft ground. She'd non-coincidentally ended up on top of his belly, straddling him. Sweat dripped from her lithe body. “Yes! Finally!” She gave little moan. “Do me right now!”

“Easy there, Dashie.” Blaze grabbed her hips, preventing her from rubbing herself against his belly. “Did you know, Boomie just got his cutie mark.”

“He did?” She glanced at him, then returned her full attention to Blaze.

He nodded. “Got it by doing a sonic rainboom, just like you.”

“Cool.” She didn't look at him at all this time, entirely focused on the stallion beneath her. “I was wondering what that big boom I heard was.” Her attentions were causing a reaction in Blaze, exactly the reaction she wanted. She gasped when his growing cock touched her under the tail. “Yes!”

But Blaze didn't give it to her yet. “You realize what him getting his cutie mark means, right?”

She paused her sliding for a moment, then her face lit up. “You mean I get to have him? Sweet! I bet he's totally fresh, isn't he? Never had a mare before at all!”

Boomie blushed, being talked about so frankly. He jumped when Rainbow went for him, but he'd reacted too slow.

She pinned him down on his back, legs splayed out, and she loomed over him, eating him up with her eyes – eyes that had a tendency to slide down to his crotch. “Mmm yes! Look at him, so young and spunky!” She licked her lips. “Can I taste him?”

“Not yet,” Blaze said. Boomie wasn't sure if he was happy to have pressure taken off of him, or disappointed in Dashie not getting her taste yet. Blaze stood up and shook the cloud bits off himself. “First, let's show him how it's done.”

Dash zipped back over to blaze, turned around in front of him, and dropped her front legs down into the cloud, pushing her rump up in his face and lifting her tail high. “Yes, finally! Somepony do me!”

“Come on over here.” Blaze waved Boomie over next to him.

When he got there, he stared at her; he couldn't help it. His sister, on full display, right there in front of him. He'd seen mares before, sure ... but not like this. This was different, and it was having a different effect on him. He could feel his stallionhood dropping out of his sheath as if he was going to pee, but he didn't need to pee at all... It was some other strange feeling he'd never had before.

“Now, Boomie,” Blaze said, “first, you should learn what an aroused mare looks like. Since Dashie here is starting to go into heat”— she whimpered slightly —“she's showing all the signs. First, and most obvious, look at the way she's standing, sticking her butt up and spreading her legs apart a little, getting in the most common position for rutting.” He trailed his hoof through her rainbow tail. “The next big sign is her raising her tail like this. She's giving you access, showing you her pussy, and helping to spread her scent. Can you smell it?” He took a big sniff, and his cock slapped his belly audibly. “That's the smell of a mare in heat, and there's no other like it. Now, look closely... come on, step right in and get close.” He nudged Boomie closer, then laid a hoof on Rainbow's rump, close to her mare parts. “Go on, touch her, feel how warm she is.”

Boomie raised his hoof almost all the way there, hesitated for a moment, shaking just above her short blue fur, then touched her. She was soft and very warm, but with a taut hardness concealed just beneath the softness.

“That warmth is another sign. They call it 'heat' for a reason. Now, look at her pussy. See how it's blushing red a little?”

Boomie looked close, his mouth hanging open. Rainbow Dash's nether lips were right in front of his face, bulging out slightly between her sharply curved cheeks, pouting out at him.

“Go ahead, touch it.”

What? Boomie glanced at his hoof still against her rump, then back at her slit. Could he really touch her there? It didn't seem real, but then, looking at her made it seem all too real. This wasn't some picture in a book – this was a real live mare's pussy... and he could touch it if he wanted. He was being told to touch it.

He gingerly slid his hoof across her toned ass, feeling it dip in toward her. Barely able to breathe, he brushed it lightly across her swollen lips.

They winked, flashing hot reddish pink at him and dribbling a splash of Dash's juice on his hoof before he could yank it away.

He blushed and shied away. “I'm sorry! I didn’t mean to—”

Blaze stopped him with a hoof, keeping him from backing away further. “It's fine, everything's okay. That just means she's really turned on and that she enjoyed it when you touched her.”

“Really?”

“Unh! Blaze, come on! I need it now!” Dash wiggled her hips and winked her pussy again and again.

“Look close again,” Blaze said. “You see how the skin of it is blushing red? That means she's really aroused. See that milky clear stuff leaking out each time she winks? That stuff is really slippery. It helps you get your penis inside her, and helps everything move more easily once you do.”

Boomie rubbed his hooves together, feeling where some had splattered onto him. It was very slippery.

“Mares get wet like this when they're turned on – they're getting themselves ready for sex. It has a really distinct flavor, and each mare is a little different.”

Flavor? Boomie had never thought of tasting it. Why would he do that?

“Go ahead, give it a lick.”

Boomie raised his hoof up, staring at the thin sheen of moisture on it. What would it taste like? It was worth it for curiosity's sake, he supposed, if nothing else.

Blaze pushed Boomie's hoof back down. “No, no. Get a little right from the source. She'll enjoy it, I promise.”

“Blazey! Now!” Rainbow whined.

Blaze patted her rump, making her tail shoot up even higher, arching over her back. “Easy there, Dashie. We've got to make sure we teach Boomie well, right? That way he'll be able to take care of you, too.”

She responed with just a whimper. Her pussy lips winked again, flashing deep reddish pink at them. Blaze nodded to Boomie and gestured toward her.

Tentatively, Boomie stepped closer, craning his neck forward as if to keep his body as far away from her as possible when he licked. He was close; he could smell her arousal. It was really strange being this close to a mare's private parts. He could see every detail of her – the smooth and full-looking lower swell of her slit, the way it thinned as it went up and wrinkled around the edges at the top. Those little wrinkles, he realized with a twitch of his cock, were there to let her stretch wide around a stallion's thingy.

“Go on,” Blaze prodded, “it's fine.”

Suddenly, impulsively, before he lost his nerve, Boomie dove in and planted a big lick from the bottom of her slit to the top.

She winked right into his mouth, making him jump back. He could taste her flavor, musky and sweet and a little bitter. It was unlike anything he'd ever tasted before. “She did that thing right in my mouth!” he cried.

“It's okay.” Blaze nudged him back in. “That's called 'winking', and it just means she likes what you're doing. Try it again. This time, if she winks, just stay in there and try to lick the bottom part of her that juts out at you.”

Boomie nodded. It was weird, but he knew that learning this stuff was an important part of becoming an adult, so he didn't want to miss anything. He leaned in again, and licked her, more slowly this time.

Dash gasped, and she winked again. This time, Boomie didn't pull back, instead, he darted down like Blaze had told him to and licked at the pink fleshy bulge that popped out whenever she winked.

Dash gave a yelp of pleasure, and a huge wave of her slippery juices washed over Boomie's tongue. He licked her a few more times, then pulled back, licking his own lips clean of her.

“Good work,” Blaze said. “She really liked that. That little bulging bit is her clit. It's pretty much the most sensitive part of any mare. But it's time we moved on to giving a mare in heat the one thing that will truly satisfy her.”

“You're telling me!” Dash yelled back at him. “It's been time for a long time now!”

“Oh hush. I know you're enjoying this.” Blaze pushed Boomie back away from her a little. “Okay, Boomie. This is where the mating really gets going. You just watch closely while I get her started, okay?”

Boomie nodded and watched... as if he hadn't been staring at Dash's pussy already.

“First, you rear up and get on top of her...” Blaze jumped up and landed his chest on top of Dash's rump. “Try and hook her tail around one of your hooves and pull it up as you go, that way it won't fall down and get tangled up. Trust me, you don't want to find out what it's like to have a few tail hairs wrapped around your junk while you're trying to do it.”

This was a little more complicated than Boomie was expecting. He made careful mental notes.

“Then you slide forward until your penis touches her.” Blaze slid up into position, bringing the tip of his cock up to touch against Dash's pussy, now winking constantly and soaking wet. “This can be harder than it looks. You might have to try a few times to get your aim right before you get the hang of it.” He began rubbing the tip against her. “Once you do get there, you want to rub it up and down on her pussy. That's really important because it spreads her lubrication over her lips and across your tip. If you don't, it's going to be really hard to get it inside, and it might be painful for her.”

Dash shoved herself backward, but couldn't get him inside because he went back with her expertly. “Unh! Come on, Blazey, shut up and put it in me already!”

Blaze petted her flanks. “You can see how a mare in heat gets really desperate when she's turned on. Right now, she isn't thinking of anything in the world other than getting her brother's cock inside her. It's a really terrible state, so it's our job to make sure she gets what she wants. When you're ready, you just push forward. It might be a little tight at first, but...”

Boomie watched, wide-eyed, as Dash's slit stretched and opened up, letting Blaze's wide, flat tip pop quickly inside. It surprised Boomie that it seemed to go inside the very top of her slit, not the middle. He could see a little pink gap between her lips just underneath his brother's shaft. Dash moaned and shoved herself backward again. This time, Blaze let her.

She slid down onto him, her madly winking pussy eating up inch after inch of his cock, only stopping as the little ring around the middle of it began to go inside.

“Now, Boomie, inside a mare, you'll first find a smooth, firm outer section that helps guide you in nicely. At the end of that is a really tight part that can take a lot of pressure to push through.” He pushed hard, his leg muscles bulging, and suddenly popped deeper into her. He grunted. “Yeah... Whoo... That tight spot is just like a little ring, and once you get past that, she's really soft and squishy and warm inside, and that little ring wraps around you. It kind of jerks you off with the pressure it puts, and that's really nice.”

Boomie couldn't take his eyes away as his brother sank even further into his sister, stretching her more as his widened base pressed inside.

“There. That's an insertion for you.”

Dash whimpered, trembling beneath him. Her juices trailed down her legs in waves.

“Then, you just start thrusting in and out, like this.” Blaze did so, making Dash cry out for everyone at the practice grounds to hear. “Each mare is different, but Dashie here likes it fast and deep.” He thrusted in and out slowly. “But I'm not going to give her that.”

Dash cried out at him. “No! Give it to me! I've waited too long already!”

Blaze didn't change his pace. “I'm going to get her really close to the edge and begging for cum before I give her to you.”

“Cum?” Boomie asked.

“Oh, right. I haven't explained that yet.” Blaze kept pushing himself into Dash, making her moan and twitch. “The best part about sex is getting an orgasm. When a mare gets an orgasm, her vagina clenches and she might squirt out some more of her juices, or even some pee. When you get one, your penis will pulse and white stuff called cum will come out. Orgasms feel really good for both stallions and mares, and it's pretty much the best thing you'll ever experience.” He picked up his pace a little, making little squelching noises come from Dash's pussy. “A stallion's cum is what makes a mare pregnant when she's in heat, and it's the only thing that will really satisfy her when she's in season.”

New worlds were opening up in front of Boomie.

Dash was moaning with every thrust now, pushing herself back hard against Blaze.

Blaze pulled out of her, his shaft glistening from her juices as he slid it free.

“No!” Dash cried out. “I need it!”

“You can have it in your mouth,” Blaze told her.

Dash spun around in a blur and tackled Blaze to the ground beneath her. She grabbed his cock in her hooves and shoved it harshly into her mouth, desperately shoving herself deeper and deeper onto it, her own female juices helping it slide down her throat. Boomie watched in awe as she pressed her lips to Blaze's sheath, lowering her hooves to fondle his balls as she shoved herself down hard again and again.

Blaze grunted. He grabbed Dash's mane and held her down at the deepest point, then he groaned loudly and Dash squirmed. Boomie could see her tongue licking at his sheath, which seemed to be rhythmically bulging. After a moment of this, white stuff started to leak around Dash's lips, dripping down onto Blaze.

Eventually, Blaze went limp, panting for breath, and Dash pulled off of him. More white stuff came out of her mouth, trailing down her chin. When she noticed, she used a hoof to help herself lick it up greedily.

“Whew... yeah. That feels good,” Blaze said absently.

Finished licking herself clean, Dash turned to Boomie. “Are you going to fuck me now? Please tell me you're going to fuck me! Will you come inside? Oh please!” She darted around to his side, lowering her head to look under his belly. “Oh wow! Your cock is so cute! It's like a little version of your brother's. It even has the same heart-shaped flare and everything.” She danced around. “Oh, please tell me I can have it! I love the way the point of that heart shape rubs on my G-spot!”

“Gee spot?” Boomie asked, looking over at Blaze.

Still panting for breath, Blaze waved him off. “We'll get to that later. For now, she's really close to orgasm, and I'm sure she'll get one when you come inside her. Go ahead.” He looked at Dash. “Now, Boomie is shorter than me. You're going to have to squat down and really spread your legs out wide so he can reach high enough.”

But Dash did no such thing. She jumped on Boomie, pushing him over onto his back, then she hopped up and straddled him.

“Blaze?” Boomie asked. “What's going on? What's she doing? She's not doing it the right way!”

But Blaze didn't answer. Dash slid up on Boomie, rubbing her soaked lips against his cock, rocking her hips and pushing her clit against him.

“Blaze?”

Dash slid higher. He could feel the wet warmth of her against his tip... then she slid lower again. This time, though it was different, very different. She enveloped him, wrapping him in her steamy tunnel as she easily made her way all the way down until she rested against his lap.

Boomie's eyes went wide. He could feel her on the inside, her twitching muscles, her panting breath, an amazing warm softness all over his most sensitive places. Her belly was exposed to him, showing off the long, graceful curve of it as she arched back, giving him a perfect view of her tight little teats just above where... where his cock disappeared between her legs.

Good Goddess... he was having sex, right there, at that very moment! Real sex, with a real mare, sister notwithstanding.

She grinned down at him. “Is this your first? Did I get your virginity?” She rocked back and forth a little, making them both gasp. “Mmm! I've never gotten a colt's virginity before. It feels nice!”

Experimentally, Boomie rocked his hips down, then pushed back up into her.

“Umn!” She bit her lower lip a little. “Yeah! Do that more!”

He did. Each push felt better and better as he got used to the feeling. What had been a simple burning pleasure shooting through him coalesced into more concrete feelings – the little slaps as the curves of her ass touched his thighs, her tail expertly tickling his balls, the gloriously slick sliding of her inner flesh against his shaft, the distinct ring inside her tightly squeezing him up and down...

A glance around showed him that a few ponies were looking, some with open hunger in their eyes, but most of them were just going about their usual business.

Boomie started pushing harder, feeling something build up inside him.

“Yeah!” Dash grunted. “Give me that flare! Come on! Yeah! Yeah! Aaah!”

The burning line of pressure was back, stretching all the way from his spine up to his tip deep inside Rainbow Dash. Instinctively, he pushed up as hard as he could, groaning as he pressed himself into her.

The pressure broke. He could feel himself twitching inside her over and over, the pulses running deep into her, filling his sister with his love.

Dash squealed and her body scrunched around him on the inside. “Yes!” she cried out, as a hot mix of their cum gushed out of her around his base, splattering down onto his balls and thighs. She collapsed down onto him, her chest over his face.

He held her tight around the middle, both of them still twitching, still spewing their cum to each other. Boomie struggled just to breathe as he rode out his very first orgasm.

Finally, their breathing calmed. Dash rose to her feet, letting Boomie's wilting cock drop out of her with a splash of white as it popped out. She stood next to him, nuzzling his cheek. “Thanks, Bro. I really needed that. You have no idea.”

Boomie looked into her eyes and nuzzled her back. “Any time, Dashie. Really. That was awesome.”

“It was special, too. I got to be your very first, how cool is that?” She turned around and showed him the hot mess under her tail. Her pussy winked, dripping with sticky white cum. “And you filled me up so good! I hope I get a foal from you!”

Boomie blinked. “Wait... am I going to be a daddy?”

“No, not yet.” Behind him, Blaze chuckled. “Even if you are the one who gets Dash pregnant, she's still Dad's mare, so Dad will be the official father. You won't have a baby to take care of.”

“Oh... okay.” It was a relief, but also a vague disappointment.

“When you have your own mares, though...” Blaze chuckled again, then shook his head. “Ah, there's time enough to worry about that later. How about we go home and I cook up some of my best spaghetti? I think you two have earned it.”

“Yay!” Dash trotted off toward home, seemingly oblivious of the slight trail of droplets she was leaving behind.

“Is it like that every time?” Boomie asked in awe as they moved to follow her.

“Nah.” He patted Boomie on the back. “Sometimes it's even better.”

Author's Note

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