"Remember when I said my powers could be considered semi-legendary?"

"I'm still probably going to want to figure out a way to make sure it can't kill me. There just aren't a lot of things that can, and I like to keep it that way."

"--Is now a good time to tell you that there exists a spell called Power Word: Kill."

"Yes, now is a good time to tell me that."

"Well, there does."

"And what does it do?"

"It...kills you, unless it doesn't. Whether it does or not seems to be some obscure function of how resilient you are physically and how powerful you are."

"And more is better, I assume?"

"Yeah, although given how the disjunction worked out I don't think trusting that your magic counts is the wisest plan ever."

"On the other hand, if physical resilience counts, it might just be - the wrong kind of thing in the first place."

"Might be, but given how silly my magic system is and the size of that crater..."

"Mm. I mean - trying to kill me by doing things to - this," he gestures at himself, "is like - like trying to put out a lamp by painting the walls black."

"Yeah but the spell doesn't destroy the body, is the thing, it just--turns off the aliveness."

"And the question is where it does that."

"I'm not even sure to what extent that's a meaningful question."

"I can think of some ways to experiment."

"Oh?"

"Mm... well, not until I have something to experiment on, but if I tell one of my swans 'I'm going to try to make you properly immortal, and if it doesn't work then when I test it you'll die'..."

"...Make them properly immortal?"

"...yes?"

She seems puzzled by something about this but has a hard time articulating it.

"...Why?" she finally manages.

"If I'm going to change the way my immortality works, I want to know the new version works for the intended purpose, and I'm sure not going to test it by having someone try to kill me. And I don't like that my swans burn out after a hundred and fifty years, it's a waste."

"I guess I was sort of modeling your immortality as..." she waves a hand. "Irreplicable?"

"Mm, how do you mean?"

"...If you could just make people for-real immortal I would sort of expected that to come up at some point when we were discussing the fountain of youth thing?"