Princess Celestia and Princess Luna were seated for dinner in the royal dining hall discussing the events of the day. They both looked like they always did. They were currently having some decaf tea waiting for desert when the topic of her most faithful student had come up.
“Twilight Sparkle has told that she organized a trip to the beach with her friends for tomorrow. It should be a lovely trip at this time of year.” Stopping for a quick sip of tea. “I imagine she will end up cataloging sea shells though.”
Princess Luna could not see how anypony would enjoy walking on the hot sand under the afternoon sun collecting sea-shells. “We would think she would find it too hot to be on the beach collecting sea-shells.”
Realizing the slight misunderstanding. “They are leaving tonight. The mornings by the sea are always pleasantly cool with the ever present breeze.”
“Why would she plan to visit the beach during the morning if she wanted to collect sea-shells? Did she not ask when would be the best time to go?”
Despite being looking up to Celestia like a mother, Twilight was more of capable of choosing when she would go on a trip. “No, she didn't, why would she?”
Luna sighed at the joke Celestia would likely drag her through “You personally taught her as a filly, wouldn't that include all of your duties?”
Celestia was ashamed Luna's prank appeared to be so poorly thought up. “Luna, you know that everypony is taught just what it is that we both do.”
“We just thought that maybe you forgot to include my duties that you were in charge of at the time into the curriculum.”
What could have caused Luna to bring up such a touchy subject for herself over tea. Wait when did the cake arrive. “Now Luna, you know, she knows full well about the beautiful night sky you make for us.”
Luna was beginning to get upset that the joke continued when neither party seemed to be enjoying it anymore. “We are glad you think we look good doing it, but we don't make the night sky every night just for the sake of having a night sky every night.”
The royal chef arrived with two slices of cake one chocolate moose and the other was pound cake with a banana on the side. He placed them before their respective owners. “...” Luna appeared to now be in a less than thrilled mood. Perhaps he had taken too long to prepare the dishes. As such it would not be a good time to speak up so he opted to leave.
Luna decided that the fastest way to end the false amnesia would just get to the point already. “The closest beach to Ponyville will be at high tide until noon then low tide by sunset.”
Celestia was not sure how this joke was supposed to be funny but continued to play her part “How do you know?”
Finally Luna could take no more of the pointless charade. “Dear sister your joke has gone on long enough.”
That was a clear sign that something was wrong. “What joke?”
“You know we are in charge of the tides of the sea and must do our best to protect the sailors who travel it.”
Celestia opted to eat a banana while she gathered her thoughts. Suddenly the thought of getting upset at the constant effort to protect sailors and look good doing it for years without anypony thanking her made a lot more sense. In fact sometimes ponies of the sea were heard to thank Celestia for their safe return during a dangerous voyage.
Seeing her sister's suddenly downtrodden mood Luna felt bad for ruining her sisters attempts, albeit in poor taste, at an attempt at a friendly joke. “Celestia, it is fine. We know that court is boring and you like to entertain yourself whenever possible. You must learn when it stops being a joke and becomes bullying.
“Luna, I am sorry it is just...”
“Really it is fine, dear sister. Just be more careful about choosing the subjects of your jokes.”
“No, it is not fine. I really wasn't joking and for that I am truly sorry.”
“So all this time everypony just showed me respect because we were related. Do you mean to tell us that for all this time you thought we became Nightmare Moon because no one one paid attention to my pretty picture I drew like a spoiled filly. ”
“... uh... no.”
“How could you do our royal duty for 1000 years and not even know what it was? Well, it could be worse, its not you like are my sister who was with me when we were being taught our royal duties and should remember or ignored the visits I would pay to important ships before they embarked on their voyage. Oh wait! That’s right there is no excuse for your not knowing of just what it is your sister does. It is almost as bad as claiming to love somepony but be completely unaware of the significance of their cutie mark.”
Luna stormed out of the room without ever touching her cake. Before it was somewhat understandable to never get thanked as the only ones who would go sailing often enough for them to be thankful would be unable to make the trip to the castle to thank her. Now she knew the entire reason was that no one had ever known all the hard work she did, because her sister had such a bloated ego that she couldn't even consider somepony else doing something important. It wouldn't be surprising if Celestia had no idea what it was Princess Mi Amore Cadenza did.
There was only one logical way to get over her 1000 year timeout for being a spoiled brat whose paintings were not complemented despite being put on the fridge, she must go visit the pirates who lived and died by the sea to drown herself in rum.
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Clearly the point might be lost a tad because of the 1000 word minimum.