In a Ponyville cafe, Twilight looked into Rarity's eyes. "I've been thinking about you, and why even though you're so beautiful, you don't have a stallion."
Rarity almost knocked over her teacup.
"Huh," Twilight said. "You're usually so graceful." She shrugged. "But that's beside the point. I've found the solution to your problem. All you have to do is...something about your cat."
Rarity glared at Twilight. "My CAT?"
"Yes, Opalescence. I've been reading surveys and studies, and stallions are less likely to be interested in a mare who has cats."
Rarity sniffed disdainfully. "What makes you think that's even an issue?"
Twilight blinked. "I remember how you tried to find a handsome prince at the Grand Galloping Gala. Aren't you still looking?"
Rarity sighed. "It was...a poorly thought out notion. I thought perhaps I should try to branch out."
"Branch out? What are you, a tree?"
Rarity laughed. "The notion occurred to me, that if I was ever to find a stallion I could truly love, the Gala seemed the most likely place." She shook her head. "But I should have known better."
"Because the Gala is full of conceited nobles with no sense?"
Rarity snorted. "That too, I suppose. But...stallions. Have you ever noticed that there are not a lot of regular stallion-mare couples in Ponyville? Did you ever think that P-Town is kind of...gay? Or at least a little bit different from some other towns?"
Twilight laughed. "You're making fun of me. I'm sorry I said anything about your cat."
"No," Rarity insisted, "I'm quite serious. Name me some regular straight couples in Ponyville."
Twilight said, "You've got to be kidding me. What about...the Cakes?"
Rarity nodded. "A good example. Now name another?"
Twilight thought. Why was she having any trouble at all thinking of more examples? "Ponyville has a whole schoolhouse full of foals, so they must have come from somewhere. What about their parents?"
Rarity smiled, perhaps condescendingly. "Be specific, Twilight darling. Whose parents?"
"Your and Sweetie Belle's parents?"
Rarity chuckled. "Sweetie Belle lives with me instead of our parents for a reason. Have you ever met our parents? You probably haven't, because they're practically never in Ponyville."
"What about Scootaloo's parents?" Twilight pursed her lips. "But I don't think I've ever met HER parents either."
Rarity shrugged her shoulders. "Scootaloo lives with her aunts Lofty and Holliday. Two mares living together quite happily."
"Where ARE her parents?"
"They're professional explorers. Last I heard, they were still in Shire Lanka."
"Diamond Tiara?"
"I think the only thing her parents love is MONEY. More's the pity. A pair of lucresexuals, the both of them, in a big ugly love triangle with their own pile of bits."
"What about...Apple Bloom? And Applejack!"
"Yes, that deeply concerns me. Their parents, Bright Mac and Pear Butter, were the nicest, sweetest straight couple you could ever hope to have as neighbors. Well, maybe not vanilla STRAIGHT straight...Big Mac comes by his crossdressing naturally, you might say. But pretty straight for Ponyville. And THEY were the ones the timberwolves came for and gobbled up." Rarity gently bit her lower lip. "Is there something about straight couples that timberwolves just especially dislike?"
"Rarity...I've never thought about Ponyville this way before."
Rarity nodded. "I suppose it might be a shock. But I thought somepony should tell you. Otherwise...if the timberwolves come for you too..."
Twilight sighed. She stood up, walked around the table, and grabbed Rarity, pressing her lips to the fashionista's.
When Twilight pulled her mouth back slightly, Rarity gasped. "Twilight! This is so unexpected! But not entirely unwelcome!" At other tables, ponies were already smiling and gossiping.
Twilight sighed. "It isn't working. I don't feel anything. I'm sorry, Rarity. I just hoped..."
"Hoped what, dear?"
Twilight sighed again. "I just don't feel that way. I guess I CAN'T feel that way."
Rarity frowned. "Are you telling me...you thought you HAD to be a marelover to fit into P-Town? I like to think that's not true. Unless you're worried about being eaten by timberwolves, I suppose." Rarity licked her lips. "I hope they can smell that we kissed. Maybe we'd better try it again, just to make sure."
Twilight said, "It's complicated. I guess for you to really understand, I would have to show you. But I suppose it's time I shared my secret with somepony."
Rarity nodded. "If I can't be your open lover...or your secret lover...I would still feel honored that you're willing to share your secret with me. Whatever your secret is."
Twilight grasped Rarity's hoof with her own, and gently tugged. "Let me take you to my library."
***
When Twilight had led Rarity to the center of the Ponyville Library's main reading room, Twilight went around closing up windows, curtains, and blinds. After double-checking that all windows were secured, Twilight took a sign out of a desk drawer, put it on the outside of the front door, and locked herself and Rarity inside with several keys.
Rarity looked at the locked door. "What are you going to do, Twilight?"
"I'm going to show you something. It might surprise you...but it's oh, so wonderful."
Rarity seemed nervous, glancing around inside the locked room. Her weight shifted back and forth slightly. "It's just...oh, never mind. I'm sure I can trust you. And we're here alone, right?"
Twilight smiled. "I promise, I won't invite anypony who isn't a perfect gentlepony. Or gentle enough, at least."
Rarity's eyebrows rose. "Are you quite sure, dear--"
Twilight levitated a nearly dust-free book out of the shelves. "Just let me show you." Magic swirled around her horn, and extended outwards. A cloud of swirling, glowing energy hid the book. As the cloud thinned, the book swelled, and grew extremities. Finally a pony-sized, three-dimensional paper doll stood in front of Twilight and Rarity.
Rarity blinked, and blinked again. "This is the oddest thing I've seen in MONTHS," she said.
Twilight reached out with one forehoof, and touched the paper pony's cheek. "It's been too long," she said. "Too long since we've touched each other in the special, secret ways I yearn for." Twilight winked. "And I know you yearn for me too." Twilight stepped forward, and nuzzled the life-size paper pony.
Rarity stared in shock, as Twilight and the enchanted paper became increasingly affectionate with each other.
While gripping the paper pony in a tight embrace, Twilight turned to look at Rarity. "If you want to meet somebook nice yourself...we have a whole library here to choose from. Every book has its own personality. I'm sure there's a book here who could please you VERY well."
Rarity said faintly, "I would let myself out...but I don't seem to have the keys."
"Oh," Twilight said. "My mistake. I should have planned better. I'm not used to doing this with anypony else around." She patted the bookpony affectionately. "It will take only a moment, my love. I promise."
The librarian and her unusual lover released each other. Twilight picked up the keys and let Rarity out. As Rarity left, Twilight said, "I'm so glad that you told me."
Blinking in the bright sunlight, Rarity said, "Told you what, dear?"
"I've always been afraid that if anypony knew, they would think I was a weirdo. But Ponyville is so accepting, so open, so free!" Twilight grinned. "Even about things like this. I knew I could count on you."
Twilight hugged Rarity, and went back inside, closing the door behind her. Rarity heard the locks and latches click and clatter.
Three fillies walked up. "Hi, Rarity!" Sweetie Belle, Apple Bloom, and Scootaloo greeted Sweetie's big sister.
Sweetie said, "Why is the library closed? Are you and the other Element Bearers doing a secret mission?"
Rarity fanned herself with one forehoof. "I suppose...you could say that."
"Aww!" Apple Bloom complained. "We wanted to do some research for a school project. We need a book about how to do origami." Apple Bloom looked at Rarity entreatingly. "Twilight knows so much about books and writing and stuff. Do you suppose she knows anything about origami? Like, even the real advanced stuff?"
Rarity half-collapsed, her hindquarters resting upon the ground. "A word of advice?" she said. "I wouldn't go asking Twilight if she knows anything about ADVANCED origami. Simply asking for an introductory book on the subject, one suitable for foals, should be more than enough."
Scootaloo whined, "But when's the library gonna be open? We gotta do our schoolwork!" Scootaloo jumped up and down, buzzing her wings, as if she wanted to try to peek through a high window.
Rarity shook her head. "The library is closed for a reason, Scootaloo. It's not proper to try to peep or pry. But I expect the library will be open again tomorrow, at the latest. So shoo, you three. Go work on the rest of your homework first."
As the three fillies walked away, Rarity noticed some posters in the library's windows.
"I <3 books."
"Get in touch with books!"
"Books can be very special friends."
"A good book can make me feel the way nothing else can!"
Shaking her head, Rarity staggered towards home.
Author's Note
"The Partially Enchanted Library: a RariTwi Story" 
I can try to write a 'more usual' sort of shipping story, but I guess sometimes it goes wildly off the rails and Spike runs away with the timberwolf, or something like that.
I wouldn't have it any other way. 
