She nods and walks inside. "I'm not actually an expert on cortical stacks, my specialty is biology. I don't know enough to recreate them without contact, just enough to speculate how they might interact with other species or magic."

She nods. "What about our immortality has Eva told you?"

"Not much. Just that it's too expensive for everyone to get one, and that all of them involve magic of some kind or another."

December pulls out the chain with her memory stone on it. "Has she told you about these?"

"I know a bit about the eva tree, how it stores memories, but not the exact mechanics..."

December leads Changeling deeper into the apartment, to a small sitting area with beanbags and a couch. "We've got a constructed minideity called the Thousand Stars that acts in the interests of Greater Eva and produces forks and merges when called on. As long as we can retrieve a memory crystal we can produce a new fork from it with all the memories and personality of the original, which is close enough to straight immortality for us. Care to take seat?" 

She takes a seat. "Thank you. Should I be imagining this as a Virtual Intelligence that is capable of interacting with magic- VIs are debatably sapient in that they synthesize information into a world model and perform problem-solving, but not sentient or agentic in that they have no experiential memory or preferences. They're generally not considered people."

"The Thousand Stars usually operates in that mode, but it can produce human representatives since after all it creates humans. It's programmed to maintain one of those: Evenstar, the living avatar of Greater Us."

"I think I want to fork sooner or later. It's quite a novelty to actually want something enough to work for it again. I mean, work hard specifically so I can afford a certain thing. I haven't done that in decades."

"Work out of style on your world, or were you getting by with the equivalent of takkarash minting?"

"Some of both. I did various kinds of publicity and sex work for a long while and had a lot of savings, and still have some passive income streams from that, I do consulting on finicky problems in my expertise occasionally, and most countries have basic income, good social services, or both. Admittedly I couldn't casually catch an express ship out to Jupiter before, but I mostly didn't want to."

"I'd love to hear more about your world. I take it your kind of body is common?"

She grins. "Oh, no. This body is extremely custom. A work of art. Tens of thousands of hours put into it with weird artsy design goals nobody else really wants. I have patents on it. The most common bodies are the clone army bodies with a pretty basic set of conveniences, or Sony Sameface androids - called that derisively for obvious reasons. And most people need to visit a clinic or robodoc to shapeshift."

"Oh, lovely! About your body, I mean. Some of me are doctors, it's not my specialty but it speaks to the affinity, yes? The Evatree is all custom too - we rather mirror each other."

"Are you sufficiently doctorly that I could brag a bit~?"

"I'll understand the basics at least!"

She has thousands of little DNA tricks including having basically ripped out and replaced her vascular and hormonal systems wholesale. Also her bones, muscles, her immune system, most major organs... And the way she enables the shapeshifting is incredibly complicated but basically it's tied in to the general 'robustness' and regen upgrades. It would normally lead to immediate massive cancers everywhere, and how she handles that is a whole other story.

She is having Lots Of Fun explaining this, but stops after about ten minutes. "-I'm probably boring you aren't I? We should talk about what you're interested in."

"No, go on, I'm taking notes for my doctor friend!" She taps her memory crystal. "I really admire your work, it sounds extremely technically complex. And worth applying in our world - cancer still gets people here sometimes, it's not infectious so Remove Disease won't cure it."

"Is that - gameable - I don't understand the rules of magic, would something that destroys cancer but is itself infectious in theory be a workable solution, for example?"

"That might work! It might be destroyed by Remove Disease still but you could always reintroduce it, it ought to work. It's very dependent on the exact effect of the spell, it's all special cases on the artificery side, sucks to work with."

"Yes, the idea was be something that destroys cancer and would go on to kill you, but, Remove Disease. I have some vague ideas about how it might work, though honestly it's a decade research project for a team of a hundred and several VIs..."

"Even if it takes a decade it would be worth it," says December. "The category of... teratogenic? Sorry I'm not a doctor - noninfectious diseases - is one of our major killers still. Cancer is one of the most common killers. We can somewhat prevent cancer with the use of Ka, but if you live long enough there's a lot of time to build up carcinogens, and once the body is compromised badly enough the only recourse we have is to replace it - which isn't casual for us."

"It sounds like there might be more low hanging fruit, from my world's perspective. Life extension treatments. And we do grow bodies."

"I'm really excited for the introduction! Do you know anything about how Cortical Stacks work?"

"The computing side of things is not my expertise, but I'm pretty well up on how they interface with the body... I've customized mine so I have internal sensors as a new sense on the same 'surfaces' you'd add, say, magnetoreception or an internal clock or a vehicle status jack-in."