"Tia?"
Little Luna slowly crept into her older sisters bedroom, framing herself in the doorway while watching her sister hard at work trying to work the sewing machine. Celestia liked making things, but had never been very good at it. Scraps of fabric littered the ground all around her, and mismatched portions were set precariously on the sewing table.
"Tia, can I talk to you?" Her voice sounded nervous, and she bit down on her lip in an adorably nervous pout.
"I'm busy, Luna," Celestia said. "I fell far behind on my projects while we were on vacation. What do you want?" She didn't mean to sound rude, and of course usually made time for her sibling, but hadn't had any time to herself all week. The two had been dragged along on a trip to visit foreign dignitaries, and it was boring as sin.
"Well, it's my fish," Luna said. "He won't wake up. I poked him a whole bunch of times."
Celestia froze instantly. Oh, Tartarus.
"Didn't you arrange for him to be fed while we were gone?" She asked. Maybe the fish was just in a coma or something.
"No," Luna said.
Celestia gasped. "Luna! You can't just not feed him!"
"I fed him!" Luna protested. "I gave him a week's sprinkles before we left!"
Celestia's heart sank. "Luna, honey, it doesn't work like that. He's a fish. He's not gonna know what to do with a week's worth of sprinkles. He's either going to eat it all at once and then not have any, or eat a little bit and the rest is gonna go bad."
"How come?" Luna asked.
"Because he doesn't think like us."
"How come?" She asked again.
"Because he doesn't," Celestia said, and turned off her sewing machine. She moved over towards Luna, and nudged her out into the hall. "Come on, let me see."
Luna escorted her older sibling to the next room, and Celestia entered. The small bowl that Luna kept her fish in was slightly green from a week's worth of neglect, and old bits of food were clumped floating at the top. Next to a motionless orange fish of decent size, which floated near the edge of the water.
Celestia frowned. Luna had only had the thing about three weeks, after winning it at the fair. "And you fed him every day?" She asked.
"Uh huh."
"And how often did you clean the bowl?"
Luna stared blankly.
Celestia sighed.
"How come he's not wakin' up?" Luna asked.
Celestia brushed part of her mane out of her eyes, glancing at the bowl. "He's not going to wake up, Luna," she said gently. "He's dead."
Luna started sniffling, and turned to look at the bowl. "Well... maybe we can make him un-dead," she offered.
"No, it doesn't work like that," Celestia said gently. "He's gone, nothing we can do about that. We're gonna have to flush him, and then maybe we can get you a new fish."
"But I don't want a new fish! I want this one! I was trying to teach him tricks!"
Celestia's horn took hold of the bowl, and lifted it off the dresser.
"I'm sorry, Luna, there's nothing we can do here. Come on." She began carrying the bowl down the hall, with Luna chasing after her, the little filly crying with tears streaming down her face.
"Maybe he's just really tired, he could wake up!" Luna protested.
Celestia continued onward, taking the bowl into the bathroom. She placed the bowl next to the toilet, which was scarcely more than a dark hole in the ground.
"We have to let him go, Luna, do you want to do it?"
"No!" Luna protested. "...Yes... are you sure we can't bring him back?"
"Ponykind cannot gain anything without first giving something in return. To obtain it, something of equal value must be lost," she recited. "There is nothing equivalent to a life that we can give. Especially not for something as replaceable as a fish. I'm sorry, Luna, I am, but you do have to learn to take better care of your things."
"Okay..." Luna said, and tipped the bowl over into the dark abyss, watching her fish disappear. As soon as she realized what she'd done, tears filled her eyes once more and she flung herself into Celestia's front legs. "I'm sorry, Tia, I didn't mean it!"
"I know, honey," Celestia said. "But we'll get you another one soon and you'll get a little better, and the fish will live a little longer. And you'll learn."
"And I can teach it to jump through rings of fire?"
Celestia blinked several times, but smiled regardless. "Of course, Luna," she said.
"Of course."