Not very good klaxons. Not that it matters, because they're quickly transformed back into cloudfluff.

The new angel finds themself near a couple of other angels playing chess plus a third one watching.

"What the fuck," one of the players asks in a language not spoken on Earth.

Words in English appear on the surface of the cocoon in a disorderly jumble, many blurry or partially merged with others: "Help". "Pain", "New", "Empiricism", "Klaxon", "Move", "see", "Guide", "Help"...

Well that's alarming. None of the angels there speaks English natively, but the third one takes summons so she can.

"Can you hear me?" she asks in English, approaching the—coffin? "You shouldn't be in pain, did you do anything—"

The words "Muffled" and "Volume (sound)" appear, then a tube presumably for the purpose of conducing sound opens in one side. A moment later, the cocoon except for text turns a slightly cloudy transparent, revealing the new angel floating now in a sort-of upright position, the hand in front of it a gelatin-suspended coral-like mess of exposed nerves, bone shards, tree-like veins, and half-formed tentacles.

One of the angels says something in that weird language that sounds like heavy cursing.

"Stop changing your body!" the English speaker says, and grabs some cloudfuff to also write out these words. "Just let it heal."

"NO IT SUCKS is BAD :(" scrawls itself in an angry red which immediately after forming stars dissolving as the syrupy substance the dye appeared within shifts as a only mostly laminar flow. 

"I can teach you to change it later, safely, without doing that, I do it all the time!"

"nO  i almo st gOT THis why Wait ? 's just a hAND ... now now NOW ick goNE???"

"Because—" And her body starts changing, she has had a few decades (more like over a century) to practice this, and...

"—I know what I'm doing and you don't."

That only seems to encourage them, and suddenly all at once their skin and large chunks of flesh melts away into syrup like burnt plastic, followed by layers below swelling up resulting in something that looks like a teleportation accident between an autopsy and a badly melted realdoll made from ballistic gel.

"oW BUrns!"

"Stop—doing—that! I can change you if you let me."

(The other two angels surreptitiously take their game and fly off.)

Much neater text appears saying thus: "Oh. Yes please! Shoggot? Just whatever is as far from this you can do easily so I have somewhere to live while learning? Something that's easy to customize?"

"Okay, yes, just let yourself heal."

She turns herself back into a female and starts turning the stuff inside the new angel's—coffin thing—into air.

The mentioned angel rapidly replaces the anesthetic-doped neutral-buoyancy saline to try to avoid the extreme pain touching air right now would be while trying to in between add text to it explaining such.

"Let yourself heal it'll be fast I swear, you're indestructible and immortal, just. Relax."

More text:

"Being immersed in water will prevent that?"

"No, it won't, you don't actually need to breathe to survive, just don't change anything and your mind should do the rest, but there's no need for you to be in the water."

After about two minutes of just trying to relax in the creepily organic shaped bathtub the thing is nominally human, although minimally so with thin skin and no hair.

"...wow you look terrible I get why you want to change, d'you have anything in mind you want to look like or?"

"Just whatever is the most different from this as possible. Maybe something feminine with lots of tentacles and easy customization?"

"...I don't actually know how to make you functional nonhuman parts—other than wings, I can do the wings—but I could do female. Just—I might need to cut you open for that, to, like, be able to look at internals and stuff, I don't know your body as well as I know mine, I've had centuries..."

"Sure that works"

"Okay, but I'm not gonna do that right here out in the open, I'm gonna take you to my place, yeah?"

"Nah I want to get rid of this right away, lets set up a tent."

"I—fine, cm'ere," she sighs, and flies a bit off the small square they're in and starts making a tent out of cloudfluff.

The cocoon thing grows wheels powered by basic springs that makes it roll into the tent. 

She waits for the new angel to have that done before saying, "You got a pretty good grasp over these powers, I took a while longer than that to get the gist of it." She starts building an operating table—crude and simple, she doesn't need too many doodads.

"I had a lot of time to practice visualizing things, and just thinking..."

A stick pokes itself out of the coffin at an odd angle, pushing against the floor and flipping the coffin over violently, spilling salty water all over and making the patient onto the table like a dead fish. Their skin promptly turns transparent, blood becomes much thicker and syrupy, and with a bit of focus tissues layer by layer inwards just slightly dissolve more as an easily tractable marker for no longer being indestructible than anything else. 

"—you don't need to do that, just, don't be indestructible and let me do the changes."

*does that*

"Thank you. You can't get knocked out because then you can't keep yourself destructible for the process but it'll be painless."

Medical training: let's use you. It will take a few hours, and will indeed be painless. And mind-numbingly boring.

It takes about 20 seconds before magenta gets bored and ask what the holdup is while shifting an eyelid hair into something that might with a lot of charity be called a periscope to see what's going on. This is followed by a bunch of rapid questions about if they can help, and how does all this work anyway?

Before they can complete turning their eyelid into—whatever, Kaede doesn't wait until it's clear—Kaede asks what they want and provides a better-supported set of mirrors to show her work and starts explaining what she's doing as she does it: she needs to change these organs, these blood vessels are supposed to connect here, these nerves have been changed away because otherwise they'd be in mind-numbing pain, et cetera.

(And no they should not help unless they have the necessary training, which they apparently don't and even if they did it's better not to do it on oneself until one has practice doing it on other people, trust her, she knows what she's doing, she's done this hundreds of times, she has several decades' worth of doing this.)

Still in text, this time on the bed: "I messed myself up pretty much as badly as possible back there and the healing is good enough that it was barely an inconvenience. Wouldn't just learning by trial and error be a lot faster? Guess I might need checklist to not entirely *miss* stuff, but still?"

"Not in my experience, no, there are millions more ways of getting this wrong than of getting this right. The healing thing does mean this is easier and neater for you, and there won't be a recovery period or bandages or swollen appendages or what-have-you, and maybe I'm being a bit conservative here out of habit, but you wouldn't be able to figure out how to change your body into a functional alternative in the same time I'm taking to do it."

"What are the rules and limitations of this stuff anyway? I mean, the obvious ones I haven't figured out myself already slash are common knowledge on earth. Mostly asking so I can break them. :p"

"Pretty sure you can't break them, and I've tried. Limitations in matter per second, can't make minds—even demons, if they try making a person they get a braindead person—can't make magical stuff like what Fairyland has or anything that breaks laws of physics, can't make antimatter."

"That's kinda the stuff common knowledge of earth, I meant the technicalities I need to know now that I'm actually *doing* it, preferably efficiently. Bet I can break the minds one though, although the obvious ways take at least decades of work. Speaking of which, looks like you're being really through and going for maximum realism and functionality there huh?"

"Most of the people I've changed were humans, I have habits, but I'm leaving as much up to the healing as I can."

The surgery doesn't take too long, as such things go, and while Kaede performs it and explains what she's doing, the new angel asks some questions and experiments with what—she?—can. After the anatomical changes are over with, the rest is mostly cosmetic, and then Kaede's done.

She changes a bit of cloudfluff into a mirror and says, "Voilà."

The changes are as per new angel's specifications: much shorter than most people (not short enough to make brain size become a problem), looking extremely feminine, with a beautiful face and athletic body. Also her skin is cyan.

Magenta pops out of whatever meditative exercise she spent the last 5 minutes of the operation in in probably way more suddenly than is recommended and attempts to sit up, failing.

"Um, this still doesn't work" appears in sort of panicky scrawled text.

"Erm, it should, were you physically disabled in life or...?"