Spike had laid out the letter on one of the library's podiums in preparation for Twilight's return. It was still there when Sanguine read it.
"Dear Twlight Sparkle,
"Sometimes things come along which are so useful they seem necessary, even if they are wrong. When this happens, silly fillies may need friends to rescue them from themselves. Even thousand year old silly fillies are not immune.
"Were she to remain in my service, I have no doubt that it would only be a matter of time before I was tempted again, so I remand judgment on the remainder of Sanguine Spray's sentence to you.
"Your humbled mentor,
Princess Celestia"
Sanguine scowled at the letter, as if it were capable of reaction. "'NECESSARY'?"
Twilight blinked. "...that's what sets you off? Not her handing you to me?" And not her brushing aside the Spike secrecy problem, Twilight noted, though that did not directly involve Sanguine.
Sanguine shrugged. "I was a royal servant, and now I am a royal servant. And I like working for you a lot more than I liked working for Celestia."
The lavender alicorn rolled her eyes. "I am not making you my handmaiden. Besides, I've already got Spike."
Said dragon poked his head into the main room of the library from the back room. "It's time to get dinner started. Is she staying?"
Twilight shook her head. "No. I'm going to need to think about this."
"Got it." Spike ducked back into the back.
"Uh, Spike?" Sanguine followed him. "Mind if I help?"
Spike looked up, momentarily unprepared for not-Twilight company but his mind soon spooling up how to deal with other ponies. Caught by the dissonance, he reflected for a moment how he had lived with Twilight for so long, she felt almost like an extension of himself in some ways - then he remembered there was another pony who had just asked him a question. "I dunno, Twilight likes her food juuust-"
"MindifIwatch?"
Spike had heard that tone before, usually from Twilight when she wanted an excuse to escape Celestia's surveillance. "...suuure, sure, you can watch. C'mon," He waved her to follow as he returned to the small kitchen.
Twilight returned to studying the letter as Spike and Sanguine left her line of sight, wondering if it contained any hidden, encoded messages.
Spike closed the door behind himself and Sanguine, then set to work getting ingredients out. "So, what's up?"
Sanguine sat by the door, recognizing food preparation just enough to know to stay out of the way. "What's it like to be Twilight's brother?"
To his credit, Spike barely fumbled the lettuce. "Brother? You'd have to ask Shining Armor."
Sanguine blinked. "Who's he?"
"Former captain of the guard, now married to Princess Cadance in the Crystal Empire. Twilight's Big Brother Best Friend Forever," Spike explained.
"...oh, so you mean he's related by blood." Sanguine nodded.
Spike nodded. "Well, yeah. That's what 'brother' usually means."
Sanguine shook her head. "I meant the other sort of brother."
Spike looked back over his shoulder at her as he dumped the produce in the sink and began washing. "I don't think 'brother' is the word you mean. I'm...actually, I'm not sure what the word is for what Twilight and I are to one another. But whatever it is, I wouldn't give it up for the world."
Sanguine smiled. "So tell me."
"She's always there for me, and I'm always there for her. Well...lately I'm kinda there for Rarity sometimes, but. Like, Twilight said 'she' needs to think about that problem?" Spike shrugged. "What she means is, she'll voice thoughts out loud and I'll bounce the good ones back to her, and I'll do the same so she can bounce my good ones back. Even the bad ones, we know it's just the thoughts that are bad, we're not trying to insult each other. Or maybe one of us doesn't understand some aspect, so the other will explain - but you'd be surprised how often that turns out the one of us who thought we understood, didn't. Finding out what you don't know can be handy."
Sanguine bit her lip gently. "So you'll be discussing my fate."
"Well...yeah, I guess." Vegetables washed, Spike moved them to a cutting board. "That's the way it is."
"Oh, no, no, I'm not blaming you. I just..." Sanguine hunted for the right words for a moment. "...wanted to know, that's all."
Spike began chopping the vegetables as the discussion paused.
Eventually Sanguine asked, "Are you necessary to her?"
The dragon nearly clipped a claw.
Sanguine tilted her head.
"...no. I'm her friend," Spike eventually replied. "Companion. Not-brother. But I wouldn't call it 'necessary'. We can operate apart when we have to. Someday I'll be too big to live in the same place she lives. I am not looking forward to it. But it won't be the end of the world - just, time to move on. When it comes. I will say I am so happy I won't have to attend her funeral...well, that there'll be time for things like moving out and growing old together before that happens."
A few more chops passed in what was otherwise silence.
Spike began sweeping the sliced vegetables into a bowl. "It's that letter, isn't it? What Celestia called you."
Sanguine nodded. "Yes."
"I think 'necessary' isn't the best word for you either. More...hmm...'royal temptation'?" Sometimes Spike wondered if his egg had been used as a political pawn, to be prepared for an easy hatching by some well-connected unicorn after many common unicorns failed the "impossible" test of hatching an unprepared egg. Not that it mattered: after Twilight had hatched him, Celestia declared that he had enough of Twilight's magic in him that there was nothing for it but to have the two of them live together from then on. Compared to most dragons, Spike had had a good life at Twilight's side - and was it not Celestia herself who once said, "Living well is the best revenge"?
"'Royal temptation'?"
"Yeah!" Spike finished getting vegetables into bowl, then began mixing it with a wooden spoon. "The point of her letter is she was viewing you like an essential tool, something that could do what she couldn't otherwise do. And that was a problem. For one, 'cause you're not a tool, you're a pony! For another, 'cause the way she was using you, she thought you might snap. And a bunch of other reasons."
Sanguine blinked. "I...kind of get that? But if I can make life better for everypony then why shouldn't-"
That finally got Spike to swing around and face her, glaring. In the same motion, he stuffed the wooden spoon in her mouth. "Don't. Don't you DARE. Finish that sentence. You deserve better than that." His voice had gone from calm to on edge in a split second.
"Mmm mm, mm mm mmm m mph," Sanguine responded, somewhat less than articulately.
"No. Nuh-uh. No way, Sanguine." Spike looked into Sanguine's eyes as if attempting to drill through her skull with his stare. "Every pony's happiness matters, and that means yours too. Besides, if you went crazy then you wouldn't actually wind up helping anypony."
"Ptoo!" Sanguine spit the spoon out. "I'm not the first pony you've said that to."
"Darn right." Spike fished another wooden spoon out and finished mixing the salad, pouring on carefully measured amounts of dressing. "You know how many times Twilight's tried to go down that same path?"
"No...?" Sanguine blinked.
"Way too many." The anger - no...annoyance? Sanguine had trouble placing exactly the quality in Spike's voice that was fading; the best she could come up with was "self defense". She puzzled on this as Spike continued, "I'm not letting her go that way, and I won't let you either. Not right here, where I can stop it."
Sanguine had nothing to say to that.
"I'm serious. You matter. Every pony matters, and you're a pony, so you matter too." Salad finished, Spike turned around to make sure Sanguine was not offended at the prospect that she might matter - as Twilight had been a few times after she had messed up in some big way.
"Thanks." Sanguine looked around the kitchen. "U-umm. What are you going to make her for breakfast?"
Spike shrugged. "Dunno. Haven't decided yet. She's not as picky when she's still waking up."
"Ooh!" Sanguine smiled. "Mind if I come by tomorrow morning and help?"
"Err, well..."
Sanguine recalled Apple Bloom advising that a certain look - "puppy eyes", apparently because Apple Bloom had learned it from Rarity's younger sister, who had learned it from a young diamond dog while Rarity was conducting business - often helped convince the adults in town, so she tried it. "Pleeease?"
Sure enough, Spike found his resistance faltering. "Eh, I suppose it can't hurt. I mean, how bad can you possibly-"