There's a lot of levels of immortality. In a way, I've already made you girls immortal. With a little upkeep and proper safety, you'll live forever. But you aren't invincible. I don't have that power.

I mean, I MIGHT be able to Gerry-rig something together, if I knew enough magic and had stronger reality warping abilities, but I'd be experimenting at best, and more likely just taking shots in the dark. And it wouldn't be fool-proof, just better.

There's really nothing that can make you completely invincible for any significant amount of time. Even someone like Noriko can get hurt, and hurt bad, with the right enemy. My body can die. My essence can be destroyed. It's not likely to happen, but with others of my kind doing it, it can happen.

So in the end, the best way is to have back-ups.