"I'm glad you could both make it." Umbra smiled at the two that she had felt small before. That day, she felt like the one in charge. A good feeling, but it came with responsibilities. "So I'm here to school you both. You want to open your relationship, but not bungle the one you have." She waved a hoof between the bashful Shining and the mildly uncertain Cadance. "A fine goal! And I'm glad to help."
Cadance leaned forward. "You're not a therapist. Not to offend, but why are you an authority in this?"
"While I am not any kind of licensed therapist or whatever." Umbra waved that idea away. "I've been around enough people over the years that had poly relationships, but this isn't poly." She raised a brow at Cadance. "Unless you plan on adding to you collection?"
Cadance blanched mid recoil. "No! It is not my intention to seek out any others."
"Great." Umbra didn't seem at all bothered by the topic. "Then what you two have is a lovely relationship, but you're still changing the boundaries. As caring adults that want their +1s to be happy, that means you have to lay the lines down clearly." She made a painting gesture, as if a brush were attached to her right hoof. "Because the ones you had don't quite apply anymore. Now, you did that to start, which is good! Very good. If this was a matter of cheating, we'd be having a whole other conversation."
Shining shrank as if he were being called out, to Cadance's clear confusion. "I was the one that... did things, Shining. Why do you look guilty?"
Shining cleared his throat. "Well... I was considering it, and... even approached Umbra about it."
"And I turned him down," finished Umbra without delay. "And he realized his mistake and here we are. Nobody actually did anything wrong, so far. We're here right now to avoid that. So." She stood up fully and coiled to direct her nose at her cutie mark. "We are bound by this thing. The crystal, not my ass, lovely as it is. We tried to just pretend it was a temporary 'thing', but it sure looks like we're making it more than that."
Cadance pricked up her ears. "Does that upset you? I don't want to impose on you. I know you didn't ask for this."
"I didn't. I didn't ask to be a magical pony princess either, but I'm also alright with that." She struck a pose and a smirk. "More than alright, really. So let's get to drawing those lines. First." She sank to her haunches to point a hoof at either of the other ponies there. "You two are the primaries. There can be no doubt here. I'm not even jealous. Shoot, you have a foal on the way, and they get to inherit your kingdom, um, if that's how Pony Politics works?"
Cadance blushed softly. "Well... In the old days, yes. These days, it is more often an active choice of a pony who they wish to cede their things when they wish to. In the lack of a clear statement, the child, or children, of that pony is still the default. Or the spouse, if that works out." She suddenly smiled at Shining. "Want to rule a kingdom?"
"Not if it meant you weren't in it." Shining clopped a hoof down. "That sounds like a nightmare."
"Aw." Umbra clapped her hooves together with an endeared smile. "You two are so pure! This is why I'm not even jealous. You two, primary, done deal." She turned one hoof on herself. "Me? I'm the third wheel, but one you happen to like. You both have an interest in me, very different interests."
Shining cleared his throat, sitting up tall. "I just want to be a part of things. I'm glad Cady found something she likes."
Cadance leaned over, pressing her nose to his cheek. "Thank you for that, but it was a one time thing."
Umbra rolled her eyes at that. "So you never want to be preened again?" That got a nice big blush out of Cadance. "Thought so. And Shining felt that, between us. Poor guy never had any wings, but suddenly he had two singing the praises of a good session of love and care." Her own wings fidgeted as if to remind her that they were entirely up to another session like that. "Now, just to address this, we could just stop sharing our feelings." She pointed up at her tiara, blocking her outgoing sensations already.
That got Shining darkening. "But... I like it."
"I do too," admitted Cadance, sharing in Shining's embarrassment, but the two slid closer together as if the shared admission drew them tighter. "Alright. Umbra, thank you. You are being so accommodating in this. I don't even have the proper words to describe it. Are you really alright just being 'the plus one' like that? Don't you want a pony to share a special bond with, like Shining and I?"
"I may," sang out Umbra. "But not yet. If I approach a pony, or some other fantastical creature--" She wasn't willing to write that off just yet. She already knew one that was lovely! "--then I'll start by telling them the situation I'm in. If they can't handle that, well, I'm barking up the wrong tree, as they say where I come from. Better keep looking, but I won't lie to them."
Shining rubbed at his cheek. "Just like that, huh? 'I'll Adult the situation.'"
"Yep!" Umbra nodded firmly. "Exactly that. And if they can't handle that, again, I'm obviously in the wrong place. Now, back to us." She spread her hooves towards both of them. "Let's cover the basics. Do ponies have STIs?"
Both looked quite baffled. Cadance dared to ask, "STIs?"
"Sexually Transmitted Infections," explained Umbra in clear precise syllables. "It means any sickness that a person has that another person can get by getting intimate with them. Is that a problem around here?"
Cadance cringed at the idea. "That sounds horrible! I am happy to report that I know of no such thing, and hope we never learn of them. The very idea, that love could bring illness... Like a curse..."
"Great!" Umbra was not at all put off. "That's one thing we don't have to worry about then." She made a slashing motion in the air left to right as if slicing that off an imagined list. "Time! There are fewer things that can get a poly relationship sour than one of them coming home to bed and, oops, there are people already there, using it, and they don't really want company right now."
Shining pointed at Umbra. "We could avoid that by always using your room. At least when you're involved. If you're part of it, you wouldn't be put out, and then that just can't happen."
Umbra blinked softly. "Point! That's a good point. But there's an extra thing." She nodded at either of them. "If we start doing things, the other will feel it. And that's your choice so don't even give any looks. I could block it all off but you don't wanna. Are you alright with having an important talk with someone and suddenly sexy feelings?"
Cadance sat up tall. "I respect that those were feelings you were both unprepared for and unasked for." She was looking at Umbra. "But I will not complain. I know... what that feels like."
Umbra wondered a moment if that qualified as a kink, that both of them were perfectly alright with that. "About that... I would prefer you two not spill over on me if I'm not there. Any objections to keeping that going?"
Shining raised a hoof swiftly. "You got it." A sharp salute. "I've gotten used to it."
"I'm so relieved." Cadance spread her wings wide, bringing them down on either of the two ponies she was talking to. "This is far less troublesome than I feared it would be."
And so those boundaries were set.
"And that's what I did." Umbra nodded at Shifting. "I'm officially in a polycule."
Shifting inclined her head slowly. "You have a word for that?"
"The one I just said." She poked her crystal bat of a friend. "But I promised I'd tell anyone about it before anything happened, so they'd know."
Shifting's tufted ears were atwitter. "You're going to... tell everycreature? See a pony on the street, tell them?"
Umbra laughed at the idea. "Not that far." She put an arm around Shifting, drawing them closer. "Just the ones that I'm interested in, or that seem interested in me."
That got Shifting to darken in her fuzzy cheeks. "O-oh! Oh..." Shifting looked away and back. "You knew?"
Umbra's brows came down together. "This was a secret?!" She thumped her head against Shifting, avoiding poking Shifting with her horn. "This world is so adorable at times, I can't even."
"And you're not grossed out?" Shifting's nose twitched, sniffing gently. "That I am both?"
"Right now?!" Umbra glanced down, but didn't look hard or long, eyes going back to Shifting's eyes where they belonged. "I thought that was... I don't entirely understand how you work, Shifting. You're going to have to explain it. But I'm not grossed out, more impressed." She raised a hoof to her chin, rubbing lightly. "Seriously, a functional hermaphrodite? Is that a changeling thing?"
"It's a changeling queen thing... sometimes. Uh... So, imagine it like this... A changeling queen must be female. Not debatable. In a hive, they're the one making the eggs. So... if a changeling queen grows the boy parts first before things 'click' and queen-dom is decided, they need girl parts, and they will happen, no questions asked. And, bonus, they keep the parts they already grew." She waggled her hooves weakly in the air. "Yay."
"But, being a changeling, you can be whatever. Which means, right now, gonna bet, you're all female?"
"That is my disguise," agreed Shifting, turning to display her profile. "Just a crystal bat mare! I can be whatever I want, or nothing at all. I could be a rock."
Umbra blinked rapidly at that idea. "Huh. That must feel weird, being... not alive."
"Of course I'm alive." She bopped Umbra right on the snoot. "It's just hard to move. Rocks aren't very fast... Anyway!" She sat up and back. "You're really not grossed out?"
"I'm really not." Umbra shrugged softly. "New topic!"
"New topic!" joined Shifting in a joyful cry. "How goes the arena?"
"Great!" Umbra began to box the air, bouncing on her hind legs in her playfight. "I've gotten a good grip on mining, so I'm helping get the crystal there faster, so I can put it together faster, which means we'll get an arena sometime this year instead of..." She faltered in her boxing to roll one hoof slowly. "Like five years from now."
Shifting applauded with stomps of the ground and enthusiastic hoots. "Nice, great! You make me so jealous sometimes." She crossed her arms petulantly. "You can work with crystals so easily! I have to do it all the slow way."
"Magic isn't the best way, just a speedy way," noted Umbra in a serious tone. "If you want the highest quality, you need actual work. Speaking of that." She leaned in, almost touching noses. "I'd love your help when we get to finishing bits. A little you-art on the outside would make it look so much nicer than the big slabs I'm throwing around."
"You know I'm ready!" She pounced at Umbra, the two flopping to the ground in affectionate hugs. "Just tell me when and where and I'll bring my A game."
"As if you have any other." Umbra nibbled at Shifting's furry chin, working towards her neck. "You're not one to half-ass things that I've seen."
"You have such funny words." Shifting pulled away to sit up. "Do creatures just talk like that where you're from? I could listen to it forever."