They lay together for a while, not speaking. Sunset, now in her pyjamas, rested her head against Adagio's chest, listening to her heartbeat, arms around her, stroking the bare skin of her back.

She considered saying “I love you”, but unsure if it was appropriate, decided not to.

“Adagio?”

“Hrm?”

“Just wanted to make sure you were still awake.”

Adagio squeezed her shoulder. “Just about.” Gently disentangling herself from Sunset she sat up and stretched, then stood and walked over to the window. There she was silent again, looking out onto the street with a slight crease to her brow.

“What're you thinking?” asked Sunset.

“Nothing.” Adagio shook her head. “Nothing important.” She looked round at Sunset and gave her a not-quite-convincing smile.

Something on Sunset's desk caught her attention, and she walked over to investigate. “What's this? A diary?” She flipped open a book and started leafing through the pages before Sunset could respond.

“Commonplace book. I like to write stuff down so I don't forget what I learned back in Equestria.” said Sunset. “Look through it if you want,” she added lamely.

After a moment, Adagio slowed down and was evidently reading the contents. “I like the little pictures …” she said quietly.

Sunset smiled.

“'Sirens'! Well …” Adagio turned a page. “Hah, it's us.” She frowned, then held up the page to Sunset. “No way am I that wide.”

“Yeah, but I gave you bigger tits to make up for it. Look, you even have cleavage in the picture.”

Adagio glanced at the picture, then cupped one breast in her hand. With an overdramatic pout she picked up a pen that had been beside the book on the desk and threw it at Sunset. “You are cruel, Sunset Shimmer.”

Sunset nodded, grinned, and got a wolfish smile in return.

After scanning the pages, Adagio looked up. “What's the squiggly T thing?”

“Tau nought. Thaumic permittivity.”

“Oh, right. Well, that makes things much clearer.” Adagio walked back, handed Sunset the book, and lay beside her. “Explain it to me. I'm not big on maths.”

“You're really interested?”

“You've got a picture of me in there. How could I not be?”

Sunset put an arm around Adagio and pulled her closer. Looking at the scattered equations and jargon-laden notes, she tried to remember what she'd been trying to express. “Right,” she began. “You know how you found it harder to use your magic here?”

“The energy in this world isn't the same as in Equestria,” muttered Adagio.

“Yeah, sort of. And that's all because the thaumic permittivity in this world is much higher. In other words, for a given amount of magical energy, it's harder to get an effect in this world than it would be in Equestria.” She turned to Adagio. “Does that make sense?”

Adagio nodded. “Go on.”

“I had an estimate for tau-nought before. I had to take in into account back when I … y'know.”

“Did mind-control on the whole school?”

“Yeah.”

Adagio smirked. “I'm sorry I missed that.”

Sunset sighed. “Anyway, after you'd done mind-control on the whole school, I came up with this: The Siren Equation. You were stuck because the amount of energy you used to stir up negativity was exactly the same amount of energy you could extract from that negativity, so you could never build up reserves. So using that equation, and with some research on the remains of your gems, I was able to get a clear value for tau-nought.” She smiled sheepishly. “Turns out my original estimate was pretty close.”

“Hm,” said Adagio.

“Hm?”

Adagio nuzzled her cheek. “Clever little pony,” she said softly.

“It's nothing, really.”

“Too modest, though,” said Adagio, taking the book from her and flipping though the pages again. “So is there anything in here about how to get my powers back?”

Sunset shook her head. “Nothing.”

“And you wouldn't tell me if there were …”

“No,” said Sunset. “Adagio –”

“It's fine,” said Adagio. She snapped the book shut and dropped it beside them on the bed. “I know we're not on the same side. And I'm pleased you're not lying to me about it.”

A brief, unsure silence ensued.

“What happened when you came here?”

“What?”

“Back in the park, you said you came through as sirens. But you're human now. What happened?”

Adagio nodded. “We came through as sirens, but we were bound to humans. Part of the spell that old pony used. Three children, each born with a gem in their mouth, on the same day in the same village. Became something of a local legend. Understand, I say we were bound to humans. That doesn't mean we were humans. They were independent, with their own minds and wills. We were just along for the ride – we retained our original forms, but we had to stay close to our hosts. Nobody could see us. Nobody could hear us sing. We could talk to each other, but that was all.” Adagio paused, and Sunset felt her take a deep breath. “I suppose the idea was to have us live and die as mortals.”

“But it didn't work?”

“Nope. Our hosts died, but we kept going. We ended up bound to their remains instead, which was as fun as it sounds. But here's the good part: Sonata came up with a way to free us.”

“Sonata?”

“She's smarter than she seems …” Adagio paused. “Actually, no, she isn't. Except when it comes to magic. Anyway, she came up with a spell that used the binding to create new human bodies for us. Immortal ones, after our own image, that could channel our magic. Our gems had been sitting in some old charlatan's collection, all the while quietly picking up a lifetime's worth of negativity. Just enough to power Sonata's spell.”

Adagio lay back and chewed her lip. “Aria and I … we owe a lot to Sonata. I …”

Sunset took her hand, waiting for more.

Adagio shook her head. “Forget it. It doesn't matter.” She stretched and sat up again. “Have you got any plans for the rest of night?”

“No …”

“Wanna watch a film?”

Sunset closed her eyes. Give her time. She's just not ready. “Okay,” she said. “Nothing mushy right?”

“Definitely not,” said Adagio with a smile.

Author's Notes:

So here's something of an experiment. It takes places immediately following the previous chapter. I'm worried it might be a bit too much of an infodump, but oh well. Have some headcanon.

We're also breaking away from the alternating porn structure. Chapter 7 will be clean. But to make up for it, Sunset takes the reins (so to speak) in Chapter 8.