Celestia woke up, admittedly feeling better than she had before she fell asleep. She pushed her now tangled hair out of her face and rubbed away her eyes' sleepiness. It was evening now. She had a long nap. She climbed off her bed, not at all wondering how she'd gotten there, and walked out of her room. Or she would've if she opened the door before walking into it. She rubbed her head for a moment to soothe the small pain and opened the door before walking through.
She didn't at all notice her parents nearby, who were preparing dinner for the three of them. They noticed her, however, when they heard her little footsteps trot behind them. Her mother stepped in her path, and she met her glance with drowsy eyes.
"Good evening. You slept well, I see," Eos laughed as she ran her hoof through Celestia's messy mane. In her not-quite-awake-yet state, Celestia didn't laugh. Her parents would've never believed a cute filly could look like a grumpy old mare if they hadn't seen her face so many times right after she woke up.
"Drink this." Astraios poured her some of the tea he and Eos had made to go with their dinner. She sat where she was and took the small cup from her father's magical hold into her own hooves. The tea was steaming hot, with light smoke billowing from the cup, so she blew on the drink a few times before taking a sip. Eos did her best to straighten out Celestia's mane a little with her hoof, but the tangles proved uncooperative.
The tea cooled enough for Celestia to drink it all in almost one go. Besides her mane, all signs of grogginess were gone and her eyes revealed their usual brightness. Deciding now was a time as good as any, her parents nudged her toward their small table and they sat together again. Her parents didn't bother with pseudo-cheery questions and fake excitement this time. Rather, they felt tense, but they hoped they hid it well enough for Celestia not to notice. At the same time, they pondered if she felt tense as they did. Eos cleared her throat and started off the discussion, mentally praying however it ended, the result wouldn't be another tantrum.
"Celestia, we know you're not excited, but we're going to have another foal in several months," she said gingerly, watching for her daughter's reaction. When Celestia stayed quietly focused, she continued speaking. "We don't know if we'll have a colt or a filly, but there will be a new baby around. That means a lot of things will be different."
Celestia's only response was a blink of her eyes. Eos exchanged a quick, inconspicuous glance of worry with Astraios, neither able to read her expression. But she was listening, so they took advantage of it.
"We're going to be very tired for a while and we might have less time to spend with you while the baby is very young," Astraios continued, his voice drawing his daughter's attention. "The baby's going to cry a lot and need us much of the time, and you might not sleep much either. But you'll still have your room to yourself, so you can sleep in peace."
Again, no response besides blinking her eyes. They wished they could read her mind. Was she taking it in or was she still upset? For once, those pink eyes gave them tension instead of peace. Though they said no words to each other, they shared the same thought: wondering if they underestimated her perception. Maybe she picked up on their tension after all, or maybe they weren't making as much as sense they thought. Eos sighed lightly and decided to quit skipping around the bush. Her husband's minor look of defeat hinted to her whatever she was about to say, he agreed.
"Celestia," Eos said, speaking in the same ginger tone, "things will change and it's going to be hard. You might not love the new baby at first." Eos had to pause after she said that, but she quickly resumed. "And that's okay. You can't be mean to the baby. You can't scream and stomp. You've learned better than that. But it's okay not to be excited. You can be upset. Things will change and it's not going to be fun, and you might hate being a sister. But it'll be well in the end and we'll always be here for you."
Right then, Eos saw a glint in Celestia's eyes, and the little pony inched her body over a small amount. Eos quietly, but pleasantly, gasped. She got it! She looked to her husband, wordlessly telling him to speak so Celestia could hear the assurance she needed from both of them.
"Your mother and I love you, Celestia." Her attention immediately turned back to him, and she turned her full body. "That's one thing that won't change. This new foal is going to make our family bigger. We are adding, not replacing. Do you---?"
He didn't have a chance to finish the question because Celestia thrust herself right into him. He caught her and quickly consoled her as she buried her face into his coat. Eos joined their side, gently patting their daughter's head. Just like that, it became one of those "we should've known" moments. Eos tilted Celestia's head up for her to look at both of them.
"Nothing and nopony takes your place," Eos promised her. "You're our daughter. You can't be replaced."
"We wouldn't dare think of it," Astraios assured her. "We'd never try."
That gut-punching frown slowly transformed into a sweet, familiar smile. Celestia curled up, like she were still a baby herself, and nestled into her father's embrace as deeply as she could. Astraios and Eos felt relieved, not only that they solved this problem in one day, but simply that they could be honest with their daughter, something they realized they should've done from the beginning.
By the next day, the whole matter was left behind. Celestia was still unhappy at the news, but with the start of the new day, she returned to her usual boisterous self. Eos and Astraios still worried about their incoming addition, but a little less so than they used to since first learning Eos was pregnant.
Over the next months, the couple did their best to spend extra time with Celestia. When they could reign her in from her typical mischievous antics, she would help them around their home, make food with them, watch the sunrise and stroll with them during the early morning, nap with them (though she always slept in her own bed at night), and whatever else they could think. Occasionally, they'd indulge her a little by joining her in her antics, so long as she wouldn't hurt them or herself. Her favorite game with them became "Tumble", which involved her charging headfirst into one of her parents, and the two of them tumbling about in laughter.
As Eos's belly grew heavier, Celestia did have questions and her parents would answer them honestly. They did so not only for honesty's sake, but in the hopes answering Celestia's questions would begin to ease her about becoming a sister.
"So," Celestia said one cloudy afternoon as she laid in bed with her parents and patted her mother's belly, "was I in here too?"
Eos nodded. "You got bigger and bigger too until you were ready to come out."
"And where does it come out? Do they cut you open?"
The couple exchanged an awkward glance before Eos quietly directed Celestia's attention to a private region on her small body.
"Yuck! That's nasty!" Celestia made a faux nauseous face. "I'll never do that when I get big!"
Her parents chuckled for a moment before Astraios asked, "Any more you want to know?"
"Ummm..." Celestia pondered for a few moments. "How does the baby get in there?"
"Well, your father does that," Eos answered, she and her husband blushing immensely.
"But how?"
"You're too young to know to know how, Celestia," Astraios told her, "but let's just say your mother and I play games after you go to bed. Adult games."
"Uh, okay." She would've asked further, but she was still currently scarred by the answer to her previous question. She moved on to the next one. "Mother, why do you get sick a lot? You don't play with us lots anymore." Her tone became a sad one.
"Because I am getting heavier all the time and I can't move so easily," Eos answered. "Lots of changes are happening inside me to keep the baby healthy, and it means I feel sick sometimes."
"But you're getting sick all the time," Celestia pointed out.
"I know and I don't like it either, Celestia," Eos told her. "But you can always snuggle up with me, and we can tell stories or nap together. When the baby is born, my belly will be small again."
"Why don't I have a baby in my belly? My belly is big and round too!" Celestia sat upright and poked out her belly, giving a silly smile.
"Because you just eat a lot," Astraios joked.