It did come back, eventually. A lot of time has passed- and while Roseluck still has a good number of pains left in her, Doctor Horse just removed her casts and told her all her bones are healed- she can go home.
“The pains aren’t all gone yet,” she states.
He blinks down at her, still sitting next to Roseluck on the bed. “... Or, if you want, you can stick around until they are all gone.”
“I’ll do that,” Roseluck states, and shudders. “Note to self: never stay in the Crusaders’ path.”
She looks up at her. “Huh? What happened?”
Roseluck smiles. “I think they were trying for their skate-car-ing-thing cutie marks or something yesterday. Whatever it was, it was massive, on wheels, and moving quickly through Ponyville.” She shudders. “I got smashed between it and the side of Bonbon’s Candies.” She looks down at her. “Whatever you do, always get out of their path first, then try to stop them.” Then she looks up at Nurse Redheart. “Soo… what was that… mystery treatment, again?”
Redheart smiles. “Last One,” she states, gesturing at her. “We think it’s some kind of innate ability, but, well…”
“She looks like a normal pegasus.”
“Indeed,” Doctor Horse agrees. “And yet, she can do… this.” He looks up at Roseluck. “Don’t tell Twilight, please. She may try tests that very well could kill her.”
“I’m hard to kill.”
“That’s exactly my point. She’ll try to find out how hard… and there’s really only one way to do that.” He sighs. “How are her pains?”
“Only … surface pains remain.”
“So, bruises and the like?”
She tilts her head. “Huh?”
He blinks, and raises his eyebrow. “So, you can fix what would have been a lost cause, but you don’t know what a bruise is?”
“Uh… I guess.”
He looks up at Roseluck. “How?”
“Language barrier?” Roseluck suggests.
He nods. “True, very possible. Um…” He looks at her. “Is that the case? You know what those… pains are, but can’t put them to words?”
She nods.
He rubs his chin with one hoof. “... Huh. So, how would you like to learn some medical science?”
She tilts her head. “Huh?”
“Uh… that is, what we call everything, how to help ponies heal… er, make the pains go away, that is, the normal way.”
“I can help ponies?”
She doesn’t know why the prospect of helping the entities- ponies; he’s using the term to refer to real, live entities, not just a drawing on the wall. In any case, she doesn’t know why the prospect of helping ponies is so… well, exciting. It’s…
Oh, she supposes she might. While it doesn’t make her think of the terrible right away, she somehow knows it’s directly contradictory to it.
Heh. Take that, terrible!
“Uh, yes?” Doctor Horse asks. He seems confused.
“Yes!” she declares.
“Wait,” Roseluck states suddenly, eyes widening. “Did you say a lost cause?”
He blinks. “Uh, no?”
She lets out a breath, closing her eyes and looking at the mattress. “So, I can fix what would have been a lost cause, but I don’t know what a bruise is?” She looks up. “What would have been a lost cause?”
He blinks again. “Uh… Oh, that. Sorry- and yes, I suppose I did. A rib in the heart… is not something we can normally fix. Add that we didn’t even know it was happening… and if she wasn’t here, you’d probably be dead right now.” He looks down at her. “On that note, Last One, you’ve successfully saved your first life.”
“Is anypony else like that?” she asks urgently. Roseluck is still staring at him, jaw hanging.
He blinks, looks up at Redheart. “Not off the top of my head…?”
Redheart shakes her head. “There’s plenty of badly injured patients, but none with injuries that could escalate like that.” Then she sighs. “I think.”
“You think?” he asks.
“Yes, I think. We didn’t even know her floating ribs were broken until Last One was pulling one of them out, did we?”
“Uhh….”
“We should at least be able to narrow it down to those with damaged ribs. We did know Roseluck had some broken ribs, just weren’t sure how many.”
“All her pains have gone awa-aaah!”
Roseluck’s head had resumed normal operation- and the pony had moved, snatching her into a hug. “Thank yo-Aaah!”
The sharp crack almost echoes through the room as all four ponies, herself included, freeze.
Then she carefully pulls her foreleg back from where it had landed against Roseluck’s chest when the motion had surprised her. “S-sorry,” she mumbles. “It… it’ll go away.”
Roseluck drops her, a foreleg of her own coming to the impact point. “O-ow-!”
… the pony’s head has suspended normal operation once again, she can sense. The pain she’d just made goes away while she rights herself on the mattress, then looks at her hoof.
She knows what the terrible is. At least, what part of it is.
She hurt someone.
She… hurt someone.
“Sorry,” she mutters, before she leaves.
She runs.
She’s much faster than she was last time she was running from here. She jumps into the air, beats her wings to slow herself to a hover in front of the door. Grasps the handle with a hoof, as Nurse Redheart did, turns it. Pulls on it.
The door opens.
She flicks it a little further open, drops back to the floor, and continues running.
The next door, she reaches when it’s almost closed. She catches the edge with her hoof, pulls it open. It groans strangely, cracks and snaps coming from the wall it’s attached to, as it deforms out of her way.
She runs.
Something breaks in the last door when she opens it, showering her and the ground in shiny bits of clear stuff. She ignores it and runs.
She’s in the street. She looks left, looks right. Looks forwards. Where to?
She sees the trees in the distance. She runs.
The trees look angry, somehow. Like it’s supposed to be dangerous. She doesn’t care. She runs.
She stops sensing both Nurse Redheart and Roseluck at once. She doesn’t care; Redheart’s back pain is gone, and head pain is going away. She runs.
She cannot help ponies if she hurts them. She cannot- will not- hurt them.
Something wooden moves into her path. She doesn’t know what it is; it looks like it has a jaw.
She doesn’t care. She runs. Under it.
She… She refuses to hurt ponies.
She finds something, and hides. Estimates how long she’ll live for…
A long time. A very long time.
She glances back at herself. She has a tail; it matches her hair. She looks like a pony herself.
She doesn’t care. She hurt a pony by touching her.
She cannot allow that to happen again. She will not hurt another pony.
She will not go where she can hurt another pony.
She…
She goes to sleep.