The Hall of Origin was a mystery to the humans who resided below it. Atop Mt. Cornet, it existed within a pocket dimension that was inaccessible to humans. The only way to access the hall was to open the wormhole that connected the two planes of existence to each other at the summit of Mt. Cornet, an ability only granted to legendary Pokémon.
Many legendary Pokémon, such as Mewtwo, preferred to spend time their time away from the Hall. They would roam the world on their own, or reside within their own separate dimensions. Most came and went sporadically, as they saw fit. No legendary made their residence permanent, even Arceus left on occasion. The Hall of Origin was seen by all as a headquarters, a safe residence, and a home, all rolled into one.
There are occasions where all the legendaries are present in the hall at a single time, such as for meetings. The Hall therefore had a room for every legendary to reside in while staying there, tailor made to their preferences. Thanks to it's unique magical properties, it could provide enough for everyone to live in comfort and safety. From here, Arceus ran the universe in all it's glory.
Diancie's mind was not occupied with these thoughts at the time however, and she let out a deep sigh. In a last ditch attempt to generate an idea, she let her head drop to meet with the desk. The cut, pink crystals atop her head landed with a thud. She let out a groan, though not one of pain. Her body was composed of solid rock and gemstone, making her very resilient to damage.
Rather, her groan came from her inability to generate new ideas, despite the three hours she had spent trying to come up with something new. She could use a jewel, or perhaps dazzle with a diamond blast, but this required something different. Something special.
"Hey Dia! What's up?" Mew, the ever energetic pink cat legendary, burst in through the door.
"Mew, don't do that!" Diance said in surprise, jumping out of her seat.
Frantically, she tried to hide the papers that littered her desk from the floating feline's eyesight, but the damage had been done.
"What's that? Sheet music?" Mew questioned, cocking his head curiously to the side.
"Um…yes." Diancie said, feeling her face flush. "It's about…gems! Yes, that was it, a song about gems."
She smiled unconvincingly, hoping Mew would buy it long enough to get rid of the evidence.
"That rocks!" Mew chuckled at the pun he had made. "You should show it to Meloetta!"
"No, that's okay Mew. She's probably busy." At this point, Diancie was desperate to drop the topic at hand.
"I'm sure she'd love to see it. Hey! I'll go and get her." Mew turned and prepared to leave, but Diancie quickly floated in front of him, shutting the door behind her.
"Ok Mew, you've forced my hand. The real reason I don't want to show Meloetta is that…it's about her." Diancie finished abashedly, facing away from Mew and towards the ground. "It's not done yet. It needs to be perfect." Just like her, Diancie thought to herself, blushing a bright red.
"Aww, that's so cute!" Mew practically squealed. "You two would be so adorable together!"
"Do you really think so?" Diancie asked, looking up from the floor and towards Mew.
"I know so." Mew said without a trace of doubt in his voice. "Come find me and the others later, we'd love to help." He winked as he flew out of Diancie's room, closing the door behind him.
Renewed with a fresh energy, Diancie once again took her place at the desk, and began to write.